As the movie opens, Cheech & Chong are siphoning gas from a tow truck to fill the tank of their "borrowed" car. As they drive away, Chong rolls and lights up a joint, igniting the gas fumes and causing an explosion in the car. Cheech is dropped off at a movie studio to ask a girlfriend for clean clothes, claiming his state was caused by rescuing a baby from a fire. Meanwhile, Chong returns the car to their prudish neighbor, resulting in a confrontation as the neighbor rants. Chong returns his sentiments by shooting exhaust fumes out of the house window, killing the neighbor's rose bushes. After smoking up, Chong plugs in his guitar and starts wailing away loudly, annoying the entire neighborhood. Cheech arrives, barely managing to pull the power on the amplifier. Cheech drives Chong to pick up a urine sample for his probation officer (last time, he used an unwashed mayonnaise jar; this time, his sister's urine, and she's pregnant!). While driving down the street, Cheech swerves the van causing the urine to splash all over Chong. Chong pulls out a large bag of what appears to be cocaine, refusing to share until Cheech asks to just "smell" it. Chong shoves the bag in Cheech's face, revealing it to be a bag of his laundry soap. Cheech grabs and drinks from the urine sample, spits it out, and Chong hands the urine to him again! The next morning, Cheech awakens to find the van has been stolen. The phone rings, Chong answers and hands it to Cheech, only to find that Cheech has been fired and that his employer has retrieved the van. The day continues as the guys go to the welfare office causing a ruckus as Cheech attempts to fornicate with one of the office workers on her office floor. Later, Cheech invites the worker over the house, practically pushing Chong out the front door. Upon finding that Cheech's cousin (Red) is in town, Cheech sends Chong to meet with Red. Chong finds Red arguing in a hotel lobby with Pee Wee Herman over an unpaid bill only to discover that Red is trying to get back his large duffel bag, stuffed full with marijuana buds. The two break into another room through a window, make their way to Red's room, and successfully grab Red's luggage. Meanwhile, Pee Wee has called the police and while leaving, Red records the police sirens and bullhorn comments on his boombox. The two end up at a brothel and, as they're leaving, Red plays the police sounds on his boombox, emptying the brothel completely, including a tied-up girl. She takes them to the home of her "trick" and before long, all of them, save Cheech, end up in a comedy club. Meanwhile, Cheech has fallen asleep waiting for Donna, the office worker, dreaming vividly of her. Back at the comedy club, Pee Wee Herman shows up and a riot ensues. As Red & Chong leave, Chong complains that they left the herb behind. Red takes Chong to one of his marijuana fields to get more with the police in hot pursuit. The police set off the booby-traps as Red and Chong are abducted by aliens. Back at the house, Donna shows up while Cheech is dreaming that the neighbor has interrupted his fun. He shouts out in his sleep "Get out! Get the f*** out, you f*** a**hole!" Donna, thinking he's yelling through the door at her, leaves angrily. Cheech falls back asleep, continuing to dream. Chong appears in the dream as a warlord and, upon awakening, realizes that Chong is now home, wearing a horned helmet, and holding a vial of "space coke." Cheech samples the coke and goes into a rage, tearing a hole in the side of the house and doing the same to the neighbor's house. The movie ends with Cheech & Chong flying high into the air to the great doobie in the sky.