The story is episodic, beginning with a series of pranks on fictional important international figures, an exploding cigar and a collapsing floor under a potentate's box seat in an auditorium. Mrs Peel investigates the Honorable John Cleverly Cartney, a suave, womanizing gentleman who appears to be present before, during or after these events. Lord Darcy arrives and informs Cartney that he has arranged another prank. Meanwhile, Steed sneaks into Lord Darcy's place and, after knocking out Darcy's male housekeeper, finds a pair of fake scissors made of rubber. But real scissors are used by an unnamed, faceless official opening the "International Friendship Club" on an electrified ribbon, killing him, and Steed and Mrs Peel can't arrive in time. Lord Darcy did not expect to be involved in murder, and is distraught. Steed gets him drunk and, under guise of knowing him from a party, finds out the truth. Through Darcy, Steed is introduced to the Hellfire Club, responsible for the pranks. Mrs Peel goes to visit Cartney and discovers he is leading the Hellfire Club, an organization based upon dressing up in old costumes and engaging in orgiastic rituals and which thrives in "ultimate sins" with the purpose to replicate the historic club as closely as possible. Cartney is fascinated by Mrs Peel and tries multiple times to pursue an intimacy. She refuses this but continues to keep in contact with him.