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, Mortimer-McGwyer (Carey Mulligan and Tom Basden) 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.