Father Brown is apprehensive when he receives an invitation to a party given by the recently released Uncle Mirth, a former music hall comedian, Brown helped to put in an asylum. When Brown and the other invitees arrive at the venue, a derelict warehouse, he and Mirth's brother find envelopes containing their death certificates. Inspector Mallory finds another death certificate for a second brother who had died of a heart attack outside the rectory the previous day.