After Schmidt and Jenko mess up surveillance on the biker gang they return to school. Schmidt is in too deep - and has even filled in college applications! His biggest concern is the school play and he races to get back on the stage. Jenko shows up and they fight.
The Principal has no choice but to expel them, and soon the angry Captain has no choice but to take them off Jump Street after breaking the golden rule.
That night Jenko is packing away his gear and moving out when Eric shows up and demands they get in the car with them. He takes them to a dark alley -- and brings out two guns. But then asks for their help, the fight earlier has won him over. The deal is going down on prom night.
Schmidt and Jenko get dressed up in white tuxedos for the big night they missed 7 years earlier, and arrive in a huge limo with Jenko's nerdy friends, and boxes of doves. Schmidt finally opens up about his identity to a drugged-up Molly.
They are summoned to one of the rooms to finally meet the supplier - and find out that it's Mr.Walters. The Biker gang show up and think they recognise the two cops - but soon their cover is blown when Molly shouts through the door that they're both undercover. The biker gang pull out guns and the leader tells the quiet one with the beard to take them out.
The biker approaches, then turns around and takes off his disguise -- it's Johnny Depp! Another biker also turns on the gang -- it's the original 21 Jump Street partners. There's a gunfight, the undercover bikers are shot up pretty bad.
Walters takes the money, and Molly as a hostage, and with Eric jumps into a limo.
Schmidt and Jenko chase after the remaining two bikers, and start a three-way limo chase.
Using his new science knowledge, Jenko makes a bomb out of potassium and battery acid, and tosses it into the biker limo, destroying it. Walters crashes the limo. Eric is too scared to get involved, but the teacher still has Molly.
Walters aims the gun at Schmidt, but Jenko dives in the way to protect his partner. Walters feels guilty for injuring his favourite pupil. Finally Schmidt overcomes his fear and shoots Walters - in the groin.
As the cops show up, they read Walters his Miranda rights, Schmidt kisses Molly, and they return to Jump Street as heroes.
The Captain gives them a new assignment -- this time they're going back to college.
After the credits, Jenko is in the school cupboard having a special 1-to-1 with Ms Griggs.