Life is hard, so Callum and Jordan, two emotionally unassembled young lads from Northern Ireland, start the Funboys' Fun Club: a playgroup for childish young men to engage in wholesome mucking about. But when a juice party goes awry, Callum's ultra-religious fiancée Morgan kicks them out, and the Funboys must search for a new HQ. When they come across Marty, a catatonically depressed 60-year-old, can they bring joy back to his life and prove that fun won't necessarily lead to an eternity spent in raging hellfire?