AstheFifteenthDoctor,playedbyNcutiGatwa,takesovertheTARDISforhisfirstepicadventurehewillbejoinedbyRubySunday,playedbyMillieGibson,asshemakesherdebutastheDoctor’scompanion.TheepisodeseestheDoctorcomeface-to-facewiththemythicalandmysteriousgoblinsashislifecollideswithRubySunday,playedbyMillieGibson.LittleisknownaboutRubySundayasshewasabandonedonChristmasEveasababy.Nowlivingwithhermum,Carlaandgrandmother,CherryherworldisabouttobeturnedupsidewhensheencounterstheDoctorandthetwosetoffontheirfirstadventuretogether