Wayne and Garth now do their acclaimed Friday-night TV show in an abandoned doll factory in Aurora. At the end of the broadcast, Wayne, Garth, and his friends, head into the Mirthmobile, and off to an Aerosmith concert. After the band's performance, Wayne and Garth head backstage (thanks to backstage passes), and grovel like they did to Alice Cooper. That night, Wayne has a dream where he meets Jim Morrison and a "weird naked Indian", in which Morrison tells Wayne that his destiny is to organize and put on a big concert. Dubbing the concert "Waynestock," Wayne and Garth get to work on arranging such a monumental task. Their early attempts to sign bands and sell tickets fall flat, though, and Wayne wonders if the whole thing was a good idea.
Cassandra, meanwhile, spends a lot of time out of town where she is working with record producer Mr. Big (from the first film) on recording music. Her new producer, Bobby Cahn (Christopher Walken), slowly tries to seduce her away from Wayne and Illinois. After Wayne admits that he was spying on her, Cassandra breaks off the relationship and hastily gets engaged to Bobby on the rebound. Garth meets a beautiful woman, Honey Hornee (Kim Basinger), at the laundromat, and she quickly ropes him in with her charms. Eventually, it's revealed that Honey is manipulating Garth into killing her ex-husband. Garth quickly bails on the relationship.
Back in the real world, tickets for Waynestock are finally selling but no bands have shown up. Wrestling with what to do, Wayne departs the festival grounds so he can find Cassandra, leaving Garth to keep the rowdy crowd in check. In an homage to The Graduate, Wayne travels to a church and breaks up the wedding of Cassandra and Bobby before escaping the ceremony with her. Upon returning to Waynestock, the bands still haven't shown up, so he and Garth consult Jim Morrison, who said that no one will come. They leave and
They lost their way, not knowing how to get back, and therefore die of thirst (the sad ending).
They drive their car off a cliff (the Thelma & Louise ending).
Aerosmith, The Gin Blossoms, and other bands have finally arrived, and the whole event is a huge success (the happy ending).
In the movie, Waynestock was held in Adlai Stevenson Memorial Park, in Aurora, Illinois. The acts that Wayne booked included Crucial Taunt (Tia Carrere and band), Aerosmith, Rip Taylor, Pearl Jam, and Van Halen. Aerosmith performs "Shut Up and Dance" at the concert. Additionally, the Gin Blossoms and Nash Kato (of Urge Overkill) can be seen being escorted out of a limousine-length Mirthmobile by the weird naked Indian as the closing credits begin.