It is Young Mr. Grace's birthday, and the staff sing the traditional birthday song for him and enjoy the traditional free lunch. They later rehearse their cabaret performance for Young Mr. Grace's birthday party, a ballet called The Ballet of the Toys. A professional cabaret troupe will also be performing at the party, and when the troupe arrives, it turns out they themselves will be performing The Ballet of the Toys, which forces the staff to go to Plan B. (thetvdb.com)