The Ballad of Wallis Island follows Charles (Tim Key), an eccentric lottery winner who lives alone on a remote island and dreams of getting his favorite musicians, McGwyer Mortimer (Tom Basden and Carey Mulligan) back together. His fantasy quickly turns into reality when the bandmates and former lovers accept his invitation to play a private show at his home on Wallis Island. Old tensions resurface as Charles tries desperately to salvage his dream gig.