The TARDIS materializes on Cranleigh Halt Station on 11 June 1925. Lord Cranleigh’s chauffeur has been expecting a famous cricketer known as the Doctor. The time-travellers are taken to Cranleigh Manor, where Lord Cranleigh (Michael Cochrane) offers the Doctor and his companions costumes for the annual ball. They meet Ann Talbot (Sarah Sutton) Lord Cranleigh’s fiancée, who looks identical to Nyssa.
Tegan admires a black orchid, which Lady Cranleigh (Barbara Murray) says was found by her son George on the Orinoco River in Brazil. Tegan recognizes George Cranleigh as a famous botanist and explorer, who never returned from the jungle. Ann was his fiancée then. Meanwhile, a bound figure struggles in his bonds in an upstairs bedroom, while a South American Indian tries to control him. The Indian is knocked unconscious. The Doctor picks out a Harlequin costume. Ann comes to the room and presents Tegan a dress and mask identical to hers. A figure enters the room as the Doctor prepares, leaving a secret passage open. The Doctor goes inside, and the door closes behind him. The figure takes the Harlequin costume.
The ball has begun. Lady Cranleigh speaks with the Indian, who says his friend has escaped. The Harlequin dances with Ann. The Doctor comes to a room full of botany textbooks. He finds the room where the figure was bound, a book in Portuguese, and a corpse. The Harlequin grabs Ann’s wrist. She screams and the man fights with a butler trying to help. The Harlequin strangles him and Ann faints. The Doctor finds Lady Cranleigh in the secret room with the Indian named Latoni (Admed Khalil). The Doctor shows them the corpse, one of the servants. She asks the Doctor not to tell the guests. The figure returns the Harlequin costume, then goes to the room where Ann is lying, revealing his deformed face to the viewers. Ann awakens and flees into the room occupied by Lady Cranleigh and Latoni, who advances on the deformed figure with a rope.
The servants inform Lord Cranleigh of recent events. He finds the dead butler and Ann’s mask. The Doctor arrives in the Harlequin costume and Ann identifies him as her attacker. The Doctor protests that there must be two such costumes, but Lady Cranleigh will not confirm that. Sir Robert questions the Doctor, who says he is a Time-Lord. He mentions the other body but Lady Cranleigh will not confirm that either.
He shows Sir Robert the cupboard, but the body has been replaced by a doll. The Lord receives a phone-call that says the cricketeer Doctor missed his train. The Doctor is arrested for murder. He is driven to the police station, where they find the TARDIS. Lady Cranleigh finally tells Lord Cranleigh about the other body, proving the Doctor’s innocence. In the secret room, the bound figure slips out of the ropes and kills Latoni. Unable to get out of the locked room, he sets a fire.
The Doctor invites Sir Robert and the Police Sergeant into the TARDIS, proving his assertions. The Doctor uses the TARDIS to return to Cranleigh Hall. The deformed figure breaks out of the blazing room and kidnaps Nyssa. Lady Cranleigh reveals the man is her missing son George (Gareth Milne). George’s tongue was removed by the Orinoco Indians because he had stolen their sacred Black Orchid. He lost his mind in the jungle and was rescued by Latoni’s tribe. George carries Nyssa to the roof. The Doctor and Lord Cranleigh reach them there. George is implored to look down and see the real Ann. He releases Nyssa but falls to his death.
This was one of the rare two-episode stories, and the first historical (that is, non-SF) story on Doctor Who since the Second Doctor’s Highlander in 1966. Peter Davison and Janet Fielding disliked it because of the lack of SF content. Sarah Sutton, presumably, enjoyed playing two characters, and reviews were positive about the change of pace and the Agatha Christie vibe. Peter Davison got to play cricket in his Doctor Who costume and is said to have been quite good. Adric basically did nothing but eat at the buffet. Most of the regular cast were not thrilled with the story, but much of that might have been because the weather turned nasty and they had to appear to be enjoying a party on the terrace in the cold wind and rain.