Robert "Fish" Fishman, a drummer who was kicked out of the burgeoning rock band Vesuvius in the 1980s, spends the next two decades living a mundane life, still bitter about his lost opportunity. When Fish's nephew, Matt, invites him to drum for his high school band, A.D.D., for a prom gig, Fish reluctantly agrees. His over-the-top presence and outdated rocker attitude initially clash with the band, consisting of the shy Matt on keyboards, introverted singer Curtis, and punk rebel bassist Amelia. However, Fish's passion and enthusiasm begin to reinvigorate the band, pushing them to take their music more seriously and record a demo. After a video of Fish hilariously drumming naked goes viral, A.D.D. gains unexpected attention and finds themselves on the brink of a breakthrough.

The sudden rise in popularity lands A.D.D. a record deal and a tour, but Fish's antics continue to test his relationship with the younger band members and create tension. As the group navigates the challenges of fame and internal dynamics, Fish is faced with a choice between his rock-and-roll dreams and the relationships he values. Meanwhile, secrets from his past and unresolved issues with his former Vesuvius bandmates threaten to overshadow the band's journey to success. The band's determination and Fish's quest for redemption provide the backbone for the chaos and comedy that ensues.