While Charlie waits for an answer to the question he popped to Amita, Don and his team try to hunt down a sniper intent on killing someone under FBI protection.

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Mathematics used: Unexpected hanging paradox and Barberpole illusion

Two members of a unit led by Don's former mentor are killed during a shootout with bank robbers. The bank robbers refuse to take responsibility of the killings and Charlie recreates the shootout to find out how they died while Don must face up to the fact that his former mentor may be dirty.

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Mathematics used: Triangulation

To find the person behind a deadly gambling ring that is running a high-stakes Russian roulette tournament, Don and his team are called in to investigate. Elsewhere, Don and Charlie become concerned over Alan's financial health.

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Mathematics used: IP traceback

The team investigates several deaths that turn out to be copies of a soon-to-be-released movie, while Larry goes on his own personal adventure. Alan continues his job search.

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Mathematics used: Triangulation

The team attempts to find the daughter of a geneticist whom they suspect was kidnapped by the unstable mother. However, they become concerned about the case when they find evidence that suggests the young girl was a clone. Meanwhile, Charlie and Amita discuss having kids and Liz reveals a dark secret.

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Mathematics used: Wavelets, Acoustics and Cake cutting

A woman's corpse turns up at a decommissioned air base.

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Mathematics used: Electric Fields for Three Point Charges, Cyclotrons and Gaussian Laser Modes

In order to find a cyber crime lord, the team conducts an undercover sting. The operation is prevented by a brilliant hacker whose goal is to take over the Internet black market. However, his actions put him in a dangerous online war that might lead to murder.

In the middle of a case where he is tracking down a criminal in charge of a heroin ring inside a prison, Agent Ian Edgerton unexpectedly turns into the murder suspect when the informant he meets with winds up dead, sending Edgerton over the edge when he takes a member of Don's team hostage.

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Mathematics used: Pursuit-evasion, Game theory and Ultimatum game

When robbers hit a diamond exchange and take hostages, Don and the team find an unlikely ally in convict John Buckley, who may help the team's investigation when they believe the men are copying Buckley's criminal strategies.

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Mathematics used: Packet injection, Man-in-the-middle attack and Combinatorial game theory (on hare games)

Agent Roger Bloom, who worked on the Cooper case, is brought in to help the team when they foil a robbery of an armored car full of Federal Reserve money and recover bills that trace back to the infamous D.B. Cooper heist.

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Mathematics used: Probabilistic risk assessment

The team investigates the theft of scratch-off lottery tickets, but the stakes are raised when one of the culprits killed at a botched robbery turns out to be a former lottery winner.

The team searches for a lost shipment of high-caliber firearms when one of the weapons is responsible for random killings throughout the city. Also, Charlie and Amita disagree on a wedding date while Don re-evaluates his relationship with Robin.

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Mathematics used: Reverse trajectory, 4D mapping, Combinatorial optimization and Pigeonhole principle

The team searches for a serial killer who is targeting men that solicit prostitutes. Also, Colby and Nikki deal with the aftermath of a car crash when they have an accident during the investigation.

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Mathematics used: Geo-profiling and Scaled gradient projection

The team gets a taste of the limelight when they search for jewels worth millions that have been stolen during an awards show broadcast. In addition, Don revisits an old case that is haunting him, and Larry returns from his adventure in the desert.

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Mathematics used: Retrograde analysis and Crowd flux dynamics

The team investigates the deaths of two men who were part of a group of friends that had been sexually assaulted by a teacher when they were young boys.

The team try to find Don's stolen gun, which is being used in a series of vigilante killings. Meanwhile, Charlie and Amita get married and Don decides on the direction he wants to take in life.