Mona Dearly can’t unlock her car so, as her keys fit her son’s Yugo, she takes that and drives off. On a bend, the brakes fail completely and she drives off a cliff into the Hudson River. Clarence, fishing in the river, sees it happen. Chief Wyatt Rash observes there are no skid marks on the road.
Her long-suffering husband Phil and son Jeph, show no grief when learning of Mona’s death, an abusive, belligerent heavy drinker, loved by none. (Jeph is more concerned about his car.) Ellie Rash (Wyatt’s daughter) wants to celebrate as the Dearlys treated her fiancé (and Jeph’s business partner) Bobby badly. JB Landscaping is not doing well due to Jeph’s laziness and poor behavior.
Phil and Rona, who are having an affair, meet at the Charm Motel. He expresses happiness about Mona’s death but denies involvement. Bobby meets Murph, his older brother, who has been helping him financially. Murph suspects he had a hand in Mona’s death. Wyatt’s investigation takes him to Jeph, who claims that Bobby threatened and attacked Mona.
Lucinda, the local mechanic specializing in Yugos, informs Wyatt that the car Mona was driving had been tampered with in multiple ways. Phil tells Wyatt he had been a battered husband, as Mona suspected he was having an affair. He also claims Jeph and Mona had an argument on the evening before the accident.
Bobby tells Wyatt he hated Mona and that they had an argument over Jeph’s pay. She would not let him dissolve the partnership unless Bobby bought them out. Phil and Jeph leave Mona’s wake very early. Wyatt breaks into the Dearlys’ and finds that Mona’s and Jeph’s car keys had been switched. Phil expresses his gratitude to Bobby for killing Mona.
Bobby then confesses to Ellie that he rigged Jeph’s car, as Jeph was destroying their business. She then announces she is pregnant. Phil tells Wyatt he spotted Bobby near the Dearly residence on the night before the accident. Jeph, who is also involved with Rona, finds out about Phil’s affair with her.
Murph tells Ellie that Bobby, who left their house that night, might have had a hand in Phil’s death. When Rona finds out, she tries to leave town. It turns out Jeph did not help Phil when he fell into the water after he threatened to expose him, Rona, and Bobby.
Police learn that Jeph is threatening suicide because of Rona’s leaving. He reveals that a drunken Mona had unrepentantly chopped off his hand when they fought over a bottle of beer. Wyatt manages to take the gun away from Jeph. Wyatt then tells Bobby privately that Clarence confessed to killing Phil to protect him.
Clarence was watching Phil tamper with the car and switch the keys. Wyatt promises Bobby to keep quiet about his involvement as long as he takes good care of Ellie and the baby. Finally, Bobby and Ellie get married and Clarence is taken away. Watch Drowning Mona Full Movie to see how this suspenseful drama unfolds!