Billy, Sam, Paddy and Archie have been best friends ever since they were children. Now that they are in their 60s, their friendship is just as strong as ever, and they are keen to celebrate a significant change in their group. Sworn bachelor Billy is getting married to a woman half his age, so a bachelor party is in order. The four pals decide to hit Las Vegas to celebrate the last member of their quartet finally getting hitched. It sounds like a great chance to revert to their youthful ways and have a blast, but they soon discover that Las Vegas has changed, and so have they. Their voyage of self-discovery is filled with fun and raucous shenanigans as they tear up the town.