Black Orchid was the fifth story in season nineteen of Doctor Who. It was the shortest story of the season at just two parts. For the first time sinceThe Highlanders, the only science-fiction elements in this story were the TARDIS and its occupants.
It was notable for being the highest-rated story of the Davison era. It also gave Sarah Sutton a chance to play two different characters, and Davison the opportunity to actually play cricket, thereby justifying his costume.
According to the DVD commentary, none of the regular cast truly enjoyed the script — though Sutton admitted to “disliking it less” than Davison, Fielding, and Waterhouse. Collectively, they believed it to be comprised of Edwardian era stereotypes and no mystery or dramatic tension whatsoever.
The TARDIS lands in 1925 at Cranleigh Halt, a small railway station in rural England. Tegan wonders where they are and the Doctor explains their location, saying he wished to have a train set as a boy. They walk out front to fnd a chauffeur named Tanner, who says he has been waiting for the Doctor, much to his surprise, telling him he’s expected for a cricket match. Though the invitation is unexpected, the Doctor is keen to play; soon he, Adric, Nyssa and Tegan have arrived at Cranleigh Hall, home of the Cranleigh family. The Doctor is immediately put into the game, and does superbly–bringing the team back from defeat to a win and delighting Lord Charles Cranleigh, who invites the travelers to a fancy dress party that evening as thanks for a splendid performance.
After the match, the cricketers and spectators retreat to Cranleigh Hall for introductions. The Doctor is asked what his name is, but Charles explains the Doctor wishes to remain incognito. In an opulent sitting room that houses a magnificent black orchid, Lady Cranleigh laments the loss of her botanist son, George, killed on an expedition to find the rare bloom. When told that the party would be a costume party, Adric, Nyssa, and Tegan say that they do not have costumes to wear; Lady Cranleigh is confused as she believed they were already wearing costumes. While everyone asks for a drink, Lady Cranleigh wonders about Nyssa’s origins, thinking she may be from a rich family she knows, but Nyssa repeatedly asserts she is not from around there. Much to everyone’ surprise, Charles walks in with his fiancée, Ann Talbot, who is almost an exact double of Nyssa. The travelers set off to their rooms to prepare for the ball.
George provides the Doctor with a costume for the party: a harlequin suit with a full mask. The Doctor removes his frock coat and tries on the mask to see how he will look before putting the costume on his bed and heading to the bath to freshen up. Someone uses a secret passage to enter the Doctor’s room and hides nearby while the Doctor emerges from the bath with a robe over his clothes, wondering what caused the noise. He finds the secret passage and ends up locked out of his room, stuck in a secret passage. At the same time, the unknown person takes the Doctor’s costume.
Upstairs, Nyssa, Tegan, and Ann Talbot prepare for the party. Nyssa is confused on what to wear when Ann has a copy of her costume brought in for Nyssa to prank the guests as to which one of them is which. As Nyssa is unsure on how to dance at the party, Tegan decides to demonstrate the Charleston, a dance popular in 1925, for her alien friend.
In the meantime, the Doctor finds his way out of the corridor into a hidden area of the mansion. He finds closets of old clothes and books and a body in a cupboard.
Elsewhere, the Doctor’s companions are enjoying the party. Nyssa is enjoying having people guess if she is Ann or not, Tegan is loving the dancing, and Adric is enjoying the food. They begin to wonder where the Doctor is. The person who stole the harlequin costume walks out of the mansion, taking Ann in a dance.
After dancing, he leads her inside and she tries to excuse herself. However, he takes her indoors and attacks her. Ann shouts to James, a servant, for help; he tackles the figure and is strangled. Ann faints while the figure turns and closes in on her.
The Doctor finds Lady Cranleigh and her servant Latoni in one of the secret passages, and shows them the body. He agrees to not tell the guests to avoid causing panic, and returns to his room. The Doctor’s impostor carefully returns the costume. The Doctor arrives back at his room and dresses in the costume set out for him, unaware it has just been worn by a killer.
Lady Cranleigh and Latoni come to a locked door in the secret passages; on the other side of the door, Ann wakes and panics at the unfamiliar surroundings, while a mysterious figure hides under her bed. Ann runs out of the room and into the arms of Lady Cranleigh. Latoni enters the room and ties up the figure, a horribly disfigured man with dead, drooping skin on his face and no tongue.
The second body has been discovered, and the servants alert Charles and Sir Robert Muir. As the Doctor descends the stairs, Ann identifies him as her assailant. The Doctor defends himself, saying he has just put the costume on and had been lost in the secret passages of the house. However, Ann is adamant that the Doctor did attack her and kill James. The Doctor asks if “he” wore the mask while attacking. Ann confirms this and the Doctor tells her that someone may have worn an identical costume to his. However, Ann points out that she was charge of giving out the fancy dress costumes, and there was only one harlequin outfit. The Doctor then decides to save himself from persecution by explaining he had just put the costume on and that somebody else might have used it, asking Lady Cranleigh to help him establish his alibi. But Lady Cranleigh refuses to corroborate his presence in the secret corridors or the existence of the other body. Out of choices, the Doctor tells them that he is a time travelling alien and that he was mistaken for “the doctor” they needed to play cricket. They do not believe him and send him away with the police along with Nyssa, Tegan, and Adric, believing them to be accessories to his “murder”.
They stop at the railway station after the Doctor declares evidence is there,
but the TARDIS is missing and they have no choice but to go to the police station. There, a policeman declares they have found a police box which no key can open. The Doctor says that this time he can prove his story and opens the TARDIS with his key, telling everyone to get inside. Lord Crainleigh is amazed by the TARDIS and apologizes to the Doctor for his wild accusations, but there is still the matter of the murders. The Doctor tells him that the true murderer may strike again and go after Ann. Lord Cranleigh decides to head home, but the Doctor tells him he can get him there more quickly than a car and activates the TARDIS.
Back at the house, the unknown man has broken free of his restraints and set fire to his door in order to escape. The TARDIS lands right outside the mansion as Ann runs out to Sir Robert. Upstairs the unknown man breaks through his door and goes down stairs where his Charles is assuring Lady Cranleigh that he will look after Ann. As Charles approaches, telling him everything will be all right, the man backs away into the Doctor and others who just entered. In a panic, he takes Nyssa with him upstairs, into the fire. Lady Cranleigh tells Sir Robert that the scarred figure is her son George, not killed during the course of his search for the black orchid, but disfigured by a tribe that held the bloom sacred and themselves its guardians. After George’s maiming, Latoni’s tribe looked after him and brought him home, where his family preferred that he stay out of sight and pretend to be dead. Chafing under the restrictions, he only wanted to speak to Ann, his former fiancée — which was why he was stalking her.
However, the Doctor points out that he has taken Nyssa and not Ann, possibly due to his bad eyesight, and that she is in danger when he realizes his mistake.
The Doctor attempts to get to him through the house while Charles climbs up the side. They confront George on the roof. The Doctor calms George down by explaining Nyssa is the person he is holding and that Ann is below in the garden. George realises that the woman he is holding is not Ann, and returns her. Charles thanks him, and attempts to embrace his lost brother, but George recoils and falls from the roof to his death.
After attending George’s funeral, the TARDIS crew depart, but are first given parting gifts of their fancy dress costumes and a copy of George’s book, Black Orchid, by Ann and Lady Cranleigh.