Charlie Hulme (Hugo Speer), a British detective inspector, is found murdered in a locked panic room on the Caribbean island of Saint Marie owned by the Lavenders, Sarah (Coralie Audret) and James (Rupert Graves). Commissioner Selwyn Patterson demands that a UK officer investigate Charlie's death, so deadpan DI Richard Poole unwillingly flies out to Saint Marie to solve the mystery. Sgt Lily Thompson (Lenora Crichlow) and Officer Fidel Best tolerate him while Officer Dwayne Myers finds fault in his 'English' methods. Richard learns that Charlie was having an affair with Sarah Lavender, providing James with a motive to murder. Richard is convinced he has solved the case, but then James is also murdered, forcing Richard to look deeper into the case, and search for a mysterious woman seen at the house on the day of Charlie's death as well as ponder the question - how can you murder someone in a locked room?

A bride is shot through the heart with a spear gun and tumbles off a balcony just minutes after getting married, in a room to which she did not have the key. Richard teams up with new sergeant Camille to work out who would want the bride dead; he learns that no one had entered or left the fifth floor of the hotel room during the celebrations, which leads him to believe one of the party guests must be the killer. However, none seem to have concrete reasons to kill and all have alibis apart from the newlywed husband, after the maid is found strangled, Richard wonders if her cleaning in progress sign caused it all.

Richard investigates the death of June, who was strangled in her rented villa. The main suspects are Doug (June's husband and an old colleague of Richard's, whom he dislikes, from the UK), Janice (June's sister, who is the sole beneficiary of June's will) and cleaner Estelle. Richard learns Estelle is trying to sell June's stolen jewellery, but she has no real motive to kill June. When Janice recalls seeing one of the villa's owners leaving the crime scene, Richard begins to question whether June's murder is linked to a historical case back in the UK.

As Camille, Dwayne and Fidel joke about saving Richard from a university reunion, one of the reunion members finds him stabbed to death with an ice pick. DI Humphrey Goodman flies over from the UK to solve the case, but the team find him odd and they all, especially Camille, miss Richard. With the case proving sensitive to the team, Humphrey takes the lead in the investigation. He learns that one of the main suspects, Roger Sadler, held a grudge against Richard for over 25 years, but when Humphrey questions Roger, his reasons to believe he murdered Richard subside. After looking through old photographs of Richard and his friends, Humphrey successfully solves the case. The team are delighted with Humphrey, but Humphrey is left heartbroken when his wife phones him from back in the UK to tell him she has left him.

Final regular appearance of DI Richard Poole (Ben Miller)

Emma Redding is found dead in her own room at a local retirement home; her death thought to have been suicide. However, with Emma's friends and fiancé all saying that Emma had a lot to look forward to in her life, Humphrey begins to suspect that she was actually murdered. Whilst investigating Emma's murder, Humphrey is given a distraction, as his wife arrives on the island seeking a reconciliation. Humphrey decides he is happier living in Saint Marie, and once successfully solving Emma's death, confides in Fidel about his growing feelings for Camille.

A séance is held during the island's Fete Mouri festival, in an attempt to contact a murdered servant from 1850. However, while the door is closed and all the participants are holding hands, the owner of a rum distillery is murdered. The participants are convinced that the ghost of the servant has come back to kill, but Humphrey is not, and begins to seek an alternative explanation for the owner's death. Commissioner Patterson steps in to help the team following Fidel's departure from Saint Marie. Commissioner Patterson also introduces Sergeant Florence Cassell.

Humphrey is called to a hotel when a bride is found dead in her room the morning after her hen party. The team quickly establish that the bride knew her murderer, as she willingly let them into her room before she was killed. Usefully, some 8-hour candles apparently denote the time of death. Camille ponders her future in Saint Marie when she is offered a permanent job in Paris. Humphrey decides to tell Camille how he truly feels about her in an attempt to dissuade her from leaving the island, but despite this, Camille ultimately decides it is time to move away to Paris.

With Camille gone, Florence is promoted to Detective Sergeant. New officer JP Hooper joins the team on Saint Marie. The lead singer of a pop group is electrocuted when a lighting rig falls in a swimming pool, and while all the suspects were in the studio at the time of the murder, they also held a grudge against the victim, who burned down a record producer's studio over 20 years ago. As Humphrey continues to search for the evidence to pinpoint the killer, he comes across a click beetle which is not native to the island, helping him solve the case.

Tom Lewis is murdered on his boat, five miles out at sea, whilst partying with girlfriend Sophie and her friends Lucy, Hema and Rachel. All the suspects alibi each other, while Lucy also tells Humphrey that she witnessed Tom make a secret phone call and place cash into a moneybag, which has now gone missing. A button is discovered on the floor of the boat, but none of the suspects recognise it. The logo on the button links Tom to a bank in the UK. Humphrey, Dwayne, Florence and the suspects all fly over to England, where DI Jack Mooney assists them with their enquiries. As the team and Jack question the bank staff — Steve Thomas, Frank Henderson, Martin West and Dominic Green — they learn that Frank had a rendezvous with Tom before Tom died. Frank denies any knowledge of a meeting with Tom; Frank himself is then murdered.

While Humphrey investigates Frank's murder in the UK, in Saint Marie JP and Selwyn learn that Tom was smuggling rum. A memory card found by the pair reveals that Steve Thomas is Tom's son. Humphrey questions Steve, who is now the prime suspect in the murder investigation, but he then learns that two other suspects were determined to prevent Frank from signing an investment deal. Humphrey manages to eliminate Steve from the investigation, and when he uncovers a hidden family link, he solves the case with Jack. After solving the mystery, Humphrey decides he is happier back living in London with Martha. Humphrey sends Jack out to Saint Marie for a holiday as a temporary replacement and he is accompanied by his daughter, Siobhán.

After he goes swimming alone one morning, author Frank (or Francis) O'Toole's body is pulled from the sea with a knife through his heart. Prior to his death, Frank argued with his agent, Larry, over his potential switch to another agent, as Frank's books were failing to sell under Larry's agency. The number one suspect is the invisible user of a hidden boat, Otis Falconer, whom Jack and the team try to track down, but find an almost non-existent record on him until Jack realises an anagram points to his identity. Elsewhere, Dwayne meets a potential new love interest but is hampered by his temporarily sharing Jack's home.

JP's old school friend, Cordell Thomas, confesses to the murder of Eugene Jones. Jack is unconvinced that Cordell killed Eugene based on the peanut that Eugene was clenching in his fist when he died. Jack and the team then find stolen belongings of former convict Charlie Blake at Eugene's house, while also learning that Eugene's sister had issues with Eugene prior to his death. Elsewhere, Dwayne celebrates his birthday with his girlfriend, Darlene, and his father, Nelson, who pays him a visit.

Note: This episode was dedicated to guest star Larrington Walker who died before his role was completed.

When Billy Springer, the lead guitarist of a popular Saint Marie reggae band is murdered in his dressing room following a concert, Jack must solve a double murder, including a case that has haunted the Commissioner for 30 years. Meanwhile, Nelson Myers joins his son, Dwayne, and makes himself at home in the Caribbean.

Local zookeeper Xander Sheppard (Jonathan Kerrigan) is found shot in the back with a poisonous dart. The only plausible suspects are the other members of his staff – including his wife, brother, sister – all of whom were with each other at the time of death. As the investigation reveals ties to a rumoured death at the zoo years ago, the team must also break in their newest team member; Ruby Patterson (Shyko Amos), the commissioner's newly-graduated niece.

Tragedy strikes close to home, leaving the team in shock. With two victims now having met the fate of the same killer, Jack realises he must bring the case to a swift conclusion in order to prevent any further casualties. A new lead provides the team with a potential identity of the killer.

Local DJ Dezzie Dixon (Terence Maynard) is murdered in a locked room during a live broadcast of his weekly radio programme. Fellow DJ Bunny Hicks (Errol Trotman-Harewood), who has long waited to step into Dezzie's shoes, soon becomes prime suspect when his alibi fails to stand up to scrutiny. But as the baffling case tests the team's puzzle-solving skills to the limit, Jack finds himself the subject of an internal affairs investigation, led by DS Madeleine Dumas (Aude Legastelois).

While investigating the case of a man found dead in a boat, Jack has to consider whether to accept Anna's offer to join her on her trip or remain on Saint Marie. In the end, with the case solved, Jack decides not to take up Anna's offer, but learning that his daughter has graduated prompts him to return to London and his old life, having decided that his time on the island has been more the result of him running away from his life rather than moving on.

As the team investigate an apparent suicide at a hotel, they are forced to call in DI Neville Parker, a detective who suffers from several serious allergies, only for Parker to determine that the 'suicide' is actually a murder, despite the fact that there is no way for the killer to have left the room as both the room door and bathroom door were locked from the inside.

A blind actress is the only witness to her husband's murder. But can she really be trusted?

A TV reporter about to broadcast an expose on a prominent Saint Marie broadcaster is found dead in her swimming pool. DI Parker is convinced her co-host Garfield Tourné is responsible but at the time he was live on air interviewing his daughter. DS Cassell returns to the island to take up the vacant detective sergeant's position offered by Commissioner Patterson who does not mention Parker's idiosyncrasies for fear she would not accept. The commissioner keeps the team up-to-date on the whereabouts of Officer Ruby Patterson, who departed to Paris with DS Madeleine Dumas, however informs the team she will be extending her hiatus indefinitely.

An archaeologist is poisoned with arsenic during a dig and Parker soon has a suspect who confesses, however evidence points to her not being the culprit. The owners of the land also fall under suspicion as they were against the dig. The problem for Parker was how was the arsenic ingested, with no suspect evidence being found. The Commissioner advertises for a new officer and Sergeant Hooper is shocked at his choice of Marlon Pryce whom he knows only too well.

Concert Pianist Pasha Verdinikov is shot dead, while composing in his piano room. However all the suspects - Pasha's wife, Grace, their gardener, Delford, Pasha's son, Joseph, and their housekeeper, Maggie - alibi each other. The initials "A.S", found wiped in blood on a piano stool, are an important clue and lead to Aidan Shawcross, who supposedly died in a road accident two decades earlier and who had a one night stand with Grace; yet his fingerprints are on the gun that killed Pasha. The case necessitates DS Cassell going to London. Catherine, who knows the family, is attacked in her own home. Commissioner Patterson calls her daughter Camille serving in the Paris police and was a DS at St Marie.

Catherine from her hospital bed tells Neville she spoke to Pasha at the harbour. Following that lead takes the team, DS Camille Bordey standing in for Cassell, to the neighbouring island of Sainte Hélène and a hospice with the bedridden Aidan Shawcross dying of cancer; leaving the problem, who was buried 20 years ago killed by Pasha and Aidan to fake Aidan's death. Identifying the body will explain the murder of Pasha and a microwave explains the how. Things take a turn for the worse for Catherine in hospital which Camille finds difficult to handle, and she hallucinates DI Richard Poole who was murdered on the island.

Guest appearance of DS Camille Bordey (Sara Martins)

Skip Marsden is found with his dinghy on a beach with a harpoon in his chest 11 miles from where his boat was moored at sea by a buoy with four well-to-do drunken stag party members, one a spoiled young viscount soon to be married, on board. Parker and the team have to determine how Marsden ended up on the beach when his dinghy was inoperable and GPS confirmed his boat had never moved. Another problem was Marsden had dog hairs in his throat from his dog that had died two months previously. The discovery that Marsden was a drug smuggler using the fixed buoy as a drug drop complicated the crime further and a fifth person was interested in the whereabouts of the drugs.

Emmet Peterson staggers into the police station wearing a bloodstained shirt, carrying a pistol and believing that he has shot dead his best friend, businesswoman, Gardenia Dujon. Parker has his doubts after finding a crayon at the scene of the crime. Delving into Dujon's past leads to the death of her young son 15 years previously and also to blackmailer, Tarone Vincent, that her paranoid husband and 21 year old daughter only knew as a former employee. Blue varnish on the finger guard of the pistol and pictures taken at the crime scene give Parker the answer. Sergeant Hooper accepts a promotion, but a cloud hangs over the team when Trainee Officer Pryce is provoked into assaulting Vincent. Catherine prods Parker to take action regarding his feelings for Florence.

Phillip Carlton, a wealthy shipping magnate, is found dead on the beach at a Christmas party, apparently shooting himself. Things get stranger when a London cab driver, Colin Babcock, receives a Christmas card from Saint Marie claiming Carlton was murdered. This prompts Commissioner Patterson to order Detective Parker, who was about to return home to Manchester for Christmas, to investigate the family. The Commissioner also recruits retired officer Dwayne Myers to assist while Detective Sergeant Cassell is away spending time with her family. Suspects include Carlton's wife, her lover, his former wife, Carlton's daughter, and his long term employee Bruce Garrett. Things are complicated when Colin Babcock turns up in Saint Marie with the Christmas card and an attempt on his life is made. While on a video call to Florence, Neville asks her out but the computer screen freezes, which prevents him from seeing her reaction.

Gabriel Taylor is found dead, stabbed, by a telephone box in the middle of nowhere. Parker and the team discover it was the last stage of an elaborate hostage scheme. Taylor's daughter had been kidnapped and he had followed the kidnappers' instructions to the letter and his daughter was released. The phone box was the location for the final confirmation of her release after dropping off the money. Parker has to delve into the family history of a deeply religious father, a mother who was a drug user and served a prison term, a daughter and her boyfriend who was disliked by the parents, and from the mother's past a just, after 10 years, released prisoner who was her boyfriend and drug dealer and blames Taylor for his imprisonment. Florence tells Neville she cares for him but wants to be just good friends. After the mystery has been solved the team is shocked by the news that one of the innocent suspects, Otis, has been shot dead in Jamaica.

Florence has successfully infiltrated the inner circle of Miranda Priestley (Victoria Ekanoye) by posing as Celeste, a babysitter for the young Dolores. Unexpectedly, Miranda arranges for them, along with Miranda's sister Karin, to return to St Marie and visit a man named Harley Joseph. Florence witnesses Miranda and Harley arguing and then is woken by a gunshot during the night but is confronted by Miranda and told to get back to bed. The next day Harley is found dead and the team is forced to investigate while not breaking Florence's cover.

Ayana is a famous singer and former drug addict, now clean and in rehab. Ayana is found dead in her room after having an allergic reaction to aspirin which had been given to her instead of her usual medication. Darlene Curtis, Dwayne's ex-girlfriend and friend of Selwyn's, is revealed to be the one who supposedly mixed up the meds despite aspirin not being handed out. Not believing Darlene killed Ayana, the team looks to the other suspects: her mother, her doctor, other patients and her mysterious stalker. Meanwhile, Neville's sister Izzy makes a surprise visit to the island and Naomi is temporarily promoted to DS after Florence's departure, but wonders what would happen if she could stay DS permanently.

A murder is committed, apparently right under DI Parker's nose. Neville undergoes a crisis of confidence, built upon his previous failure to recognise Sophie's duplicity, and tells the commissioner he intends to leave. Neville visits Sophie in prison, where he asks if any of their relationship had been "real"; she says she never had romantic feelings for him but had come to like the character she pretended to be when she was with him, so in that sense he'd made her happy. This allows him enough closure to enable him to concentrate on the current case. Ultimately, Neville realises how the murder was carried out, and the team arrest the guilty party. Satisfied, Neville agrees to stay on Saint Marie.

A celebration of fifty years police service takes an unexpected turn for Commissioner Patterson when he is shot at the local Yacht Club. Evidence initially points to an Alton Garvey, but despite a phone call from the man himself admitting to the crime, no motive is apparent. The only suspects are Jacqueline St Clair (Cathy Tyson), a lifelong friend of the Commissioner; her husband, who suspected her of having an affair, and Marlon Collins (Sean Maguire), the Yacht Club manager - an old adversary of the Saint Marie police force, a corrupt criminal.

During this special episode, Catherine is seen alongside her daughter, Camille, who is giving birth, whilst Neville Parker and Marlon Pryce had Facetimed them to see if she knew about Marlon Collins' past after having several convictions. There is also a brief flashback to the series' first episode when Collins was arrested by DI Charlie Hulme and Sergeant Lily Thompson. Camille gives Neville a nudge, telling him to go for what he wants in life while he can. At the end, Neville opens one of his drawers and takes out a photo of DS Florence Cassell with her puppy. The scene confirms Neville still has feelings for Florence.

Famous chef, Stanley Drake, is poisoned and dies when talking to Andrina Harper Patterson, Selwyn's daughter, after a cooking competition which had showed various hopefuls who wanted to win the competition. The team, however, are left confounded when they realise that the victim didn't consume anything that day that the contestants hadn't consumed themselves. This eventually leads to 3 out of the 4 suspects being found to have plotted to murder Drake after he sexually assaulted all three of them in the past. During the episode, Catherine reunites with Lucky, an old friend in Saint Marie who abandoned her 30 years ago. Despite the estrangement, Catherine insists she would help Lucky and the others receive a lenient sentence. Selwyn is pleased when Andrina tells him she is writing an expose on Drake, designed to encourage other victims of his to come forward.

Marlon receives a mysterious phone call from his old boss, who sounds badly injured as he begs him for help. It's a blast from his criminal past, and someone he's not spoken to since joining the police force. But when he hurries over to find out what's wrong, Marlon is horrified to find his former boss lying dead - having been shot, the only witness to the incident being a parrot. Marlon is then knocked out by an unknown assailant. Marlon becomes determined to solve the case, insistent that - although his former boss dabbled in criminality - he wasn't a 'bad guy'. But when the team uncovers two potential suspects, they find themselves at a stalemate: one suspect with every opportunity but no motive, and the other with every motive but a rock-solid alibi. Meanwhile, Marlon's sister Jocelyn wins a scholarship but it is in Jamaica and Marlon feels obliged to move there with her. Marlon, who wants to continue in policing, is disappointed to find there is currently no available position in the police force there. The Commissioner goes to Jamaica and is joined by Sergeant JP Hooper; together they manage to secure an immediate position for Marlon in the Jamaican police force.

Guest appearance of Sergeant JP Hooper (Tobi Bakare)

At a swish resort on the island of Saint Marie, Cora Blyth (Gabrielle Glaister) is celebrating with her husband Joe (John Gordon Sinclair) along with their daughter, Holly (Ellise Chappell) and her husband Sam. The next morning, Joe leaves Cora alive in a lift, and she arrives at the reception floor stabbed to death. A mysterious woman, Lexi Reece tries to enter the crime scene and is pursued by Darlene and Dwayne.

To help with the increasing workload, the Commissioner introduces Officer Dwayne Myers back into the force, to a frosty reception from Darlene. Elsewhere in the episode, Neville talks to Zoe about the chance of them being back together before this is later dismissed as impossible. Neville plans to leave Saint Marie and find love, inspired by Zoe. After the team arrest Cora's killers and Holly finds her biological mother, Lexi (Ronni Ancona), Commissioner Patterson gets an unexpected phone call from Florence Cassell, who has been living on the neighbouring island of Saint Auguste under a witness protection scheme. She explains that she is out of witness protection after two years and is heading back to Saint Marie.

Return of Officer Dwayne Myers (Danny John-Jules)

Whilst Neville planned to travel and look for his soulmate on a plane to Dominica, one of the passengers (Kurt Henderson), played by Calvin Demba is murdered. DI Parker chooses to come back for one final case to solve whilst he comes to realization that Florence may be his true love and must get to the yacht she is scheduled to board before it's too late.