Plot summary

Poet Moondog lives a hedonistic and pseudo-nomadic lifestyle in and around the Florida Keys while slowly working on his new book and enjoying life as a local legend despite the common opinion that he is past his prime. His escapades are funded by his wealthy wife Minnie, to the disapproval of their soon-to-wed daughter Heather and his agent Lewis. Moondog flirts and cheats with several women he meets on his journeys, while Minnie is in a passionate affair with Moondog's friend, R&B singer Lingerie.After arriving late to Heather's wedding in Miami, Moondog gropes the groom, Frank, in front of the audience. Later, during a talk about Moondog's crude behavior, Minnie confesses her affair to her daughter (which Moondog has no knowledge of). Meanwhile, Lingerie shows Moondog a potent strain of cannabis, endemic to an isolated pond in Jamaica, which he claims to be responsible for his success.During the reception, Moondog smooths things over with Heather and Frank while they cut the cake. He later witnesses Minnie and Lingerie kissing and, in shock, swims in a fountain and then runs off. Minnie tracks down Moondog at a local bar, and the two enjoy a night of intoxicated karaoke and dancing, culminating with Minnie drunkenly driving into oncoming traffic. Moondog escapes with minor injuries, but Minnie dies in the hospital shortly after.Half of Minnie's estate goes to Heather, while Moondog's half is frozen and placed under Heather's control; she will grant it to him once he proves he can mature and finish his novel. In retaliation, and due to Lewis' refusal to book seminars for Moondog due to his work ethic, Moondog recruits a group of homeless people and trashes Minnie's mansion. To avoid prison time, he agrees to a year of rehabilitation but breaks out of the facility with a pyromaniac named Flicker. The two part ways as Moondog makes his way back to Miami.He bumps into an old friend and alleged Vietnam veteran dubbed "Captain Wack" who offers Moondog an opportunity to co-captain dolphin tours around the outer Keys. Captain Wack decides to swim with the dolphins during a tour before realizing too late that they are sharks, which sever his foot. Now back in Miami and wanted by the law, Moondog reconnects with Lingerie, who confesses to Moondog about his affair with Minnie but claims Minnie truly loved Moondog. The revelations provoke little reaction from Moondog. After Lingerie and Jimmy Buffett tell Moondog about a respective dream and experience the two had concerning cross-dressing to avoid detection, Moondog begins to do just that. The police eventually bear down on Lingerie's property, prompting Moondog to flee to Key West with Lingerie's help and an undisclosed amount of the Jamaican weed.Inspired, Moondog completes his book, a poetic memoir titled The Beach Bum. The book is universally lauded and nets Moondog a Pulitzer Prize. A newly-divorced Heather is impressed with her father's strides and unfreezes his inheritance, which Moondog demands to be in physical cash and placed on a large sailboat. During a party to celebrate his wealth, Moondog lights the money on fire, triggering several fireworks and causing an explosion. Moondog survives unscathed, but the crowd is too concerned with the raining money to care as he drifts away on a boat.