Cheech and Chong have a new business driving an ice cream truck selling "Happy Herb's Nice Dreams." However, it is not ice cream they sell, but it is marijuana, stolen from their friend Weird Jimmy whose plantation is under their beach house camouflaged as a pool. The two eventually make a fortune. They blissfully plan on becoming "Sun Kings in Paradise" which involves buying an island, guitars, and enjoying lots of women.
The police are on Cheech and Chong's tails from the start, as they trick the stoners into selling them some of their "ice cream." Sgt. Stedanko (Keach, reprising his role from Up in Smoke), now himself a stoner, tests the marijuana and slowly turns into a lizard (a side effect). Just as the police storm their house, Cheech and Chong pack up the marijuana in their truck and drive off, leaving Weird Jimmy to be arrested. While Sgt. Stedanko continues smoking their product, becoming stranger and more lizard-like, his two deputies, Det. Drooler and his inept partner Noodles, tail the stoners.
Cheech and Chong dine at a Chinese restaurant to celebrate their wealth. There, they are accosted by an annoying record agent who bothers Chong (mistaking him for Jerry Garcia), followed by Cheech's ex-girlfriend Donna (Guerrero, reprising her role from Cheech & Chong's Next Movie) and a cocaine-snorting mental patient, Howie "Hamburger Dude" (Paul Reubens). The four of them snort cocaine under the table, prompting Chong to sign away all their money to Howie for a useless check, which they are unable to cash due to none of them having an ID.
Cheech takes a drunk Donna out to her truck to have sex, but she passes out. A pair of incompetent California highway patrolmen show up, almost busting Cheech when Chong abruptly shows up in their ice cream truck. However, not wanting to deal with the impending long procedure of the arrest, the cops let Cheech and Chong go.
The two head back to Donna's apartment. While attempting a threesome, Chong leaves to get ice. At this point, Donna's crazed racist biker husband Animal shows up, having broken out of prison. Cheech tries to escape out the window and ends up climbing the hotel naked. Chong then returns to the room and hides under the bed. Eventually, Animal has sex with Donna and they fall asleep. Cheech gets back into the hotel, returns to the room, and retrieves some clothes to wear.
Cheech then realizes Chong has signed away all their money to Howie. After getting a lift from Drooler and Noodles (disguised as women), the stoners find and break into the address on the check: a mental institution. They spend the night and in the morning they find Howie among the inmates. Cheech tries to grab Howie to get their money, but the doctors believe Cheech to be another patient and lock him in a straitjacket and chained up in a padded room. Chong finds a doctor (Timothy Leary) to help, and Cheech and Chong are offered "the key to the universe" (LSD).
Chong simply passes out but Cheech endures a bizarre trip that finally ends the next morning when the head nurse awakens them. She has realized what has happened and apologizes to them, returns their money and sets them free; Howie also seemingly apologizes, but not long after he says he is not sorry and laughs. At this point, Stedanko's cops show up and arrest the head nurse and Howie instead. By now, Stedanko has become even more lizard like, complete with a tail.
With Weird Jimmy's marijuana plantation busted, Cheech and Chong resort to becoming male strippers at Club Paradise where they are billed as "The Sun Kings."Cheech Marin as Cheech
Tommy Chong as Chong "Man"
Stacy Keach as Sgt. Stedanko
Paul Reubens as Howie Hamburger Dude
Evelyn Guerrero as Donna
Peter Jason as Det. Drooler
Tim Rossovich as Noodles
Timothy Leary as Himself
Sandra Bernhard as Girl Nut
Tony Cox as Midget Nut (Credited as Joe Anthony Cox)
Michael Winslow as Superman Nut
Cheryl Smith as Group Blonde #1
Linnea Quigley as Group Blonde #2