Aging pals Billy (Michael Douglas), Paddy (Robert De Niro), Archie (Morgan Freeman) and Sam (Kevin Kline) have been best friends since childhood. When Billy finally proposes to his much-younger girlfriend, all four friends go to Las Vegas to celebrate the end of Billy's longtime bachelorhood and relive their glory days. However, the four quickly realize that the intervening decades have changed Sin City and tested their friendship in ways they had not imagined.