"Operation Mongoose" is a 2-part story comprising the twenty-second and twenty-third episodes of the fourth season of the American fantasy drama series Once Upon a Time, both of which aired on May 10, 2015. Both episodes served together as the fourth season finale.In this episode, Isaac becomes a wild card in Gold's scheme to change everyone's destiny as Emma Swan, Regina Mills, Mary Margaret, Captain Hook and David Nolan attempt to stop them.