Gumapang Ka sa Lusak (English: You Crawl in the Mud^[1]), also known internationally as Dirty Affair,^[2] is a 1990 Filipino political thriller crime drama film written by Ricky Lee and directed by Lino Brocka, both of them are conferred National Artists. It stars Dina Bonnevie, Eddie Garcia, Charo Santos, Christopher de Leon, and Allan Paule.

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Produced and distributed by Viva Films, the film tackles the abuse of power and evil acts committed by Edmundo Guatlo in which Rachel, a movie actress who is his mistress, and her friends try to expose his scandals and violent acts done by him and his henchmen to the public.^[1]

In 2010, the film was remade into a television drama series of the same name by GMA Network as the nineteenth installment of Sine Novela and starred Dennis Trillo as Levi, Jennylyn Mercado as Rachel, Al Tantay as Edmundo Guatlo, and Sandy Andolong as Rowena Guatlo.^[3]

Living in the slums of Manila, Jonathan, a college student likes to hang out with his wealthy college friends Eric, Dodo, and RJ. One night at a bar, he meets Rachel, a former sexy star who is having an affair with Mayor Edmundo Guatlo, who is running for Congress and is being supported financially by the mayor at the cost of being constantly followed by Edmundo's aide Falcon. Jonathan sees Rachel again at the bar, but when Falcon and his men force her to come with them, Jonathan helps her escape. Rachel visits her family, but her younger sister Gigi is embarrassed because of her affair with Edmundo. She also visits her former boyfriend Levi who is imprisoned for robbery. She asks Edmundo to use his connections to release Levi. While on the way to a party, Edmundo is tailed by his wife Rowena and is asked to transfer to her car. At the party, Rachel comes and surprises Rowena.

Rowena visits Rachel and offers money but asks her to leave the house that she got from Edmundo. Rachel says that Edmundo has the last say. Rowena warns her that if she does not comply, she will pour acid on her face and she will have her raped. Then, Rachel's father is fired from his work. He believes that it was Rowena who was responsible for this after she talked to his employer. Edmundo tells Rachel that Levi is about to be released from prison. Upon Levi's release, Falcon tells him that Edmundo helped him, but asks him to kill Edmundo's political rival, Atty. Ricardo Tuazon. When Rachel visits Levi, he reveals Edmundo's instructions, promising that they will start all over after the deed. Levi complies and kills Tuazon during a beauty pageant. But Edmundo betrays him and orders his men to hunt him down. Levi seeks refuge at the house of Rachel's family. But her father does not want to get involved with Levi. Jonathan also comes to help, but Rachel refuses because she does not want him to get involved. Falcon and his men arrive and kill Levi in front of Rachel and Jonathan, both of whom escape.

Rowena is furious at Falcon for not killing Rachel but is told that Edmundo ordered them not to kill her. Rowena warns that Rachel might go to Tuazon's camp and expose everything. Rachel seeks the help of Jonathan and his friends. Dodo offers her to stay in her cousin's place. While Eric, Dodo, and RJ are on the road, they are accosted by Falcon and his men. Falcon asks RJ where they brought Rachel. But, RJ fights back and is shot dead by Falcon. Falcon tells the others that he has abducted Rachel's parents and tells them to contact him if Rachel wants to see them. She then calls Edmundo, who admits that he was the one who ordered the abduction of her parents to make sure that she will contact her and tell her that she still loves her. Rachel then plays a tape-recorded confession of her saying it was Edmundo who ordered the murders of both Levi and Atty. Tuazon. She also reveals that when she was still an actress, she was abducted by Edmundo's men and taken to a resort where she was raped by Edmundo. Edmundo offered her financial support for her and her family. He also threatened her that if she disobeyed him, he would ruin her face, forcing her to leave her acting career and become Edmundo's mistress. Rachel tells him that she will make several copies and she will spread it in national media. But she says she would give the tape to Edmundo, in exchange for her parents' freedom. But, when Rachel comes to the place where her parents are, Falcon arrives. She asks where Edmundo is, but Falcon says he is not around. She is reunited with her parents and warns Falcon that she has friends. Falcon threatens them and shoots Rachel's mother after she slaps him. Falcon being held by Rachel's father distracts Falcon, allowing Rachel to escape at the cost of being shot by him asked her to escape.

During an event, Levi's mother stabs Rowena to avenge her son before being shot and killed. While Edmundo gives a speech at a rally, Rachel comes and tells everyone of his role in the assassinations. As Edmundo denies the accusations, Rachel's recorded confession is played. A furious Falcon mortally shoots Rachel, causing panic. Rachel thanks Jonathan before she dies in his arms as Edmundo and Rowena are arrested. Jonathan then looks at the sunset and reminisces his memories with Rachel.

• Dina Bonnevie as Rachel Suarez, a former movie actress who is Edmundo's mistress and wants to expose his evil acts to the public
• Christopher De Leon as Levi, Rachel's boyfriend who was tasked by Edmundo to assassinate his political rival
• Eddie Garcia as Edmundo Guatlo, a demon-minded mayor who is running for congressman and has an affair with Rachel
• Charo Santos as Rowena Guatlo, Edmundo's wife
• Bembol Roco as Falcon, Edmundo's henchman who usually watches Rachel's actions
• Allan Paule as Jonathan, a young college student who is a fan of Rachel Suarez and one of the driving forces to expose Mayor Guatlo's evil and scandalous acts to the public
• Francis Magalona as RJ, one of Jonathan's friends but kidnapped and killed by Falcon
• William Lorenzo as Eric, one of Jonathan's friends
• Timothy Diwa as Dodo
• Perla Bautista as Rachel's mother
• Anita Linda as Levi's mother
• Maureen Mauricio as a movie actress in a film set
• Ernie Zarate as Rachel's father
• Lucita Soriano as Jonathan's mother
• Ray Ventura as Atty. Ricardo Tuazon, Edmundo's political rival whom Edmundo wanted to kill him
• Archie Adamos as Rowena Guatlo's bodyguard