Set mostly over one long day and night, Lovers, Liars & Lunatics follows a dysfunctional suburban Los Angeles family. Paddy Rayne [Vic Polizos] is the manager of a local retail store who is having an affair with his secretary Gloria [Mia Cottet]. Paddy wants to leave his neurotic, highly contemptuous wife Elaine [Christine Estabrook] to live with his mistress. Unfortunately Gloria just wants Paddy's money. He hides the money at home. Gloria calls on her two "associates", Louis [Michael Muhney], and his dim-witted girlfriend Justine [Amber Benson], to rob the Raynes when the house is empty that night.
Elaine figures out the affair and steals Paddy's money from the kitchen cupboard spice bottles. She plans to leave him in the morning. Both cancel their getaway plans to Bakersfield.
Later that night, Louis and Justine arrive at the house to rob it, only to be surprised by finding Paddy and Elaine still there, forcing the inept burglars to tie them up. But soon, Louis and Justine realize they cannot leave, for their getaway car is missing (Justine had accidentally left the drive gear on), plus Paddy's other car is gone (their son Gunner had taken it for his date with Sally). Soon, the couple is bickering at each other. Louis demands to know where they keep their money. Soon, Julian [Ryan Spahn], the couple's other son, walks in and he too is soon tied up. When Gunner and a drunken Sally return from their late-night date, they are also caught at gunpoint and tied up by the increasingly desperate Louis and Justine.
Paddy, in the seclusion of a nearby bathroom, tells Louis that he will give him his wealth totaling $140,000 if he kills his wife so he can be free of her constant nagging, while Elaine later tells Louis that she will give him $15,000 of the store's retail profits if he kills Paddy's mistress, Gloria. But Elaine doesn't know that it was Gloria whom hired Louis to rob their house in the first place.
As the night drags on, the events lead to Gloria's arrival, wanting to know what is taking so long with the robbery, as well as the arrival of two persistent, but equally inept, policemen [James Charles Leary] and [Rayder Woods] who threaten to blow everything out of proportion. Justine literally shoots herself in the foot with the gun, forcing her to untie Elaine to tend to her wound. At the same time, Gloria has wild sex with Paddy in the bathroom to get to him to talk where he is keeping his money, which leads to him dying from a sudden heart attack. (Earlier that evening, Elaine had switched his heart medication with Viagra.) Gloria then learns from Louis about a $140,000 cashier's check and takes it from him. In another argument, Gloria accidentally shoots Justine, leading to chaos as Elaine takes advantage of it to untie everybody. Louis attacks Gloria, while Gunner intervenes, in which he slips and fatally hits his head against the kitchen counter. Elaine grabs a baseball bat and bludgeons Louis to death with it. While Julian flees, Sally runs outside to chase after the departing police, only to get accidentally run over by the cop car. The two policemen return to the scene, where they catch and arrest Gloria as she's leaving the house. Investigating, the two policemen find all the dead people with Elaine apparently the only one alive. But in an off-the-wall, final joke, it's strongly hinted that Elaine could get blamed for all the deaths because of her erratic personality, having been driven over the edge of sanity from this ordeal, with the final shot of her babbling to the two cops about her husband having an affair, and then she rants about not having the best TV sound speakers.
