Forty years after his first documentary about the rock band Spinal Tap, director Marty DiBergi has still not achieved fame in Hollywood, so he decides to start working on a new film about the band. He meets Hope, the daughter of the band’s former manager, who has inherited the contract with the band, and learns that they are contractually obligated to perform one more concert. Now Spinal Tap must reunite and perform for the first time in 15 years.