The film kicks off with a segment from the TV show American Success Story, which revisits the lives of its main characters since the events of the previous movie. Lou Dorchen (Rob Corddry) has transformed into a mogul thanks to his empire, Lougle, as well as his side project, the band Motley Lou. Meanwhile, Nick Webber (Craig Robinson) has found success as a musician, having created hit songs from the future before their original artists could. However, Lou's son, Jacob (Clark Duke), resents his father's fame and tries to distance himself from Lou's shadow. Nick also mentions their friend, Adam Yates (John Cusack), who has authored a bestselling book and is currently on a journey of self-discovery.
As the plot unfolds, we see Nick filming a music video for the song "Stay", which he adapted from Lisa Loeb's work and infused with his own lyrics. The actual Lisa Loeb serves as his cat wrangler and reveals the song holds significant personal meaning for her, prompting Nick to offer a silent apology for borrowing it. Lou, holding a meeting with disgruntled employees, learns from Brad (Kumail Nanjiani) that his company is failing, yet he remains oblivious to their concerns, boasting about achieving success through time travel instead.
That night, Lou throws a lavish party at his mansion, forcing Jacob to play butler. During the festivities, Jacob develops a crush on the attractive coat-check girl, Sophie (Bianca Haase), but she misinterprets his role. As Nick and Lou engage with an old classmate, Gary Winkle (Jason Jones), who is desperate for Lou's investment in his land, tensions rise. Nick’s relationship with his wife, Courtney (Kellee Stewart), is fragile as she wishes to visit her sister, but Nick's desires take precedence.
In a shocking turn of events, Lou delivers a self-centered speech that infuriates the crowd, including his wife, Kelly (Collette Wolfe). The lights abruptly go out, and gunfire erupts, leading to an unexpected injury for Lou. As chaos ensues, Nick and Jacob pull Lou upstairs, where Jacob discovers their time-traveling hot tub, combining it with a vial of nitrotrinadium to enable their trip back in time to identify Lou's assailant.
Upon awakening, they find Lou unconscious but alive, which sparks a series of misadventures as they navigate a future that has shifted in unexpected ways. Their escapades lead them to Adam's son, Adam Yates-Steadmeyer (Adam Scott), who is not aware of their connection to Lou. Amidst a blend of humorous mishaps and critical social commentary, the trio becomes embroiled in events that challenge their friendships and their very identities.
As they struggle against a series of absurd challenges that includes a misguided attempt to take down a rogue smart car, the realization dawns on them that Lou’s past decisions have irreparably altered their destinies. The film culminates in an exciting finale where they confront their issues head-on and strive to amend their past mistakes, leading to heartfelt reconciliations.
In the end, energy surges as they dial their adventures back through history, exploring the potential to reshape significant historical moments, albeit with comically unexpected outcomes. Ultimately, the film wraps up with an invitation to ongoing adventures in their trusty hot tub time machine, suggesting that this unlikely group of friends will continue to navigate the chaos of their own time-traveling realities.
