Lazy stoner and process server Dale Denton has only one reason to visit his equally lazy dealer Saul Silver: to purchase cannabis, specifically, a rare new strain called Pineapple Express that is hot on the drug market.
Saul genuinely wants to befriend him, but the selfish Dale is only interested in gaining access to the weed. When he becomes the only witness to a murder by a crooked cop and the city's most dangerous drug lord, he panics and dumps his roach of Pineapple Express at the crime scene while fleeing.
Upon returning to his dealer, he finds out the weed is so rare that it can be traced back to him. Both decide to flee and forsake the idea of calling the police, because anyone could be involved with the murder.