In an English country house two figures are seen struggling before one of them, a servant, falls dead. A young woman is seen sleeping as a figure enters her room. The figure is then seen tied to the bed guarded by an Indian with a large ring distending his lower lip.
It is June 11, 1925, and as a train departs Cranleigh Halt railway station, the TARDIS materialises. The crew disembark before receiving an explanation of the basics of the steam train from the Doctor. He says that he has always wanted to drive one. Leaving the station, they encounter the chauffeur of Charles, Lord Cranleigh, who has apparently been expecting the arrival of "the Doctor". He stares at Nyssa as if he recognises her.
They are driven to a cricket match where Lord Cranleigh's team is batting but not faring very well. Lord Cranleigh greets them and seeing Nyssa exclaims the she is exactly like his fiancée in appearance. They discuss cricket, the Doctor says that he is a fast bowler. The Doctor goes into bat and scores a plethora of runs. When Nyssa is introduced to his mother Lady Cranleigh, she also exclaims how extraordinary a resemblance between her and Ann, but is surprised that she is not a "Worcestershire Talbot" Nyssa proudly declares that she is from the Empire of Traken. The Doctor takes a turn at bowling and proves equally prodigious managing to get several players out. Lord Cranleigh congratulates him on a ripping performance and invites him home to meet his mother.
When introduced, Lady Cranleigh asks "Doctor who?" but Lord Cranleigh says he deserves to remain incognito after his fine cricketing performance. Sir Robert Muir, the chief constable of the county, also congratulates the Doctor, saying that his performance was "worthy of the Master". The Doctor looks momentarily alarmed until he explains that he is referring to "the other Doctor", W. G. Grace. Lord Cranleigh asks if they would mind staying to the annual ball - a fancy dress party - on behalf of sick children. Tegan says that they have no costumes, to which Sir Robert comments that he was thinking how charming their outfits were. Lord Cranleigh has a selection of costumes that they can use.
They are introduced to Ann Talbot, Lord Cranleigh's fiancée, and she looks identical to Nyssa. Ann also enquires if Nyssa is from Worcester, and when Nyssa says that she is from Traken, Sir Robert says that he believes it is somewhere near Esher. Ann wonders if there could be Talbots from Esher. Lady Cranleigh thinks not as the "hunt is not good enough".
When Lord Craneligh offers them a drink, the Doctor asks for lemonade. Tegan asks for a screwdriver, but when Nyssa asks for "the same" the Doctor coughs in disapproval, so instead Lord Cranleigh offers her orange juice. Nyssa tells Ann that she doesn't know where Esher is, to which Lady Cranleigh comments this demonstrates great taste, and that she should stop probing into Nyssa's background. When Tegan admires a curious black flower in the study, Lady Cranleigh explains that it is a Black Orchid and that it was found on the Orinoco by her eldest son George. Tegan recognises the name immediately as George Cranleigh, a famous botanist and explorer. Lady Cranleigh goes on to say that George never returned from his last expedition into the Brazilian forests. Ann had been engaged to George before his disappearance.
Meanwhile, the bound figure struggles against his bonds. The Indian goes to the secret room to inspect the figure, but he sees the untied ropes before he is hit on the head from behind.
The Doctor picks a Harlequin outfit to wear to the ball. When he tells Lord Cranleigh that Adric is from Alzarius, Lord Cranleigh says that he could never remember all those Baltic bits. Tegan and Nyssa discuss the Charleston, with Tegan giving a demonstration. Nyssa says that dancing on Traken is much more formalised and that she learnt how to dance as part of her training. Ann comes to their room, and presents Nyssa with a dress identical to her own, so that the ball attendees will not be able to tell them apart. Ann reveals the only difference between them is that she has a mole on her left shoulder.
As the Doctor gets himself ready for the ball, a figure enters his room from a secret passage. On hearing a noise, the Doctor returns to the room but sees no one, only the newly revealed opening. He enters the opening and finds the secret passage, but the panel slams closed behind him, trapping him. The figure reenters the Doctor's room and with his deformed hands takes away the Harlequin mask and costume.
In the gardens, the ball has now started and the guests have arrived. Nyssa asks Adric to dance with her, to his consternation, while Tegan dances with Sir Robert, who is amused by some of her colloquialisms. Lord Cranleigh is dancing with Ann. Nyssa and Ann run inside the building and emerge — now nobody knows which of them is which. They resume dancing with their partners, but Adric stops dancing saying he would rather eat. Lady Cranleigh spots the Indian and goes aside to talk to him. He informs her that his "friend" has escaped. Tegan gets to show her Charleston. When one of Ann and Nyssa starts dancing, Adric turns to the other believing it must be Nyssa as Nyssa would not know how to do that dance. She confounds him by joining in. The figure wearing the Harlequin costume arrives at the party and begins to dance with the girl that it thinks is Ann.
The Doctor finally finds his way out of the passage and finds a room full of botany textbooks. Trying to ascertain his whereabouts, he finds a staircase and ascending them he finds the secret room where the figure had been bound. Searching it, he finds a book written in Portuguese. When he leaves the room, he wanders down the corridor, examining the cupboards, and in one of them he discovers a corpse. Meanwhile the Harlequin figure enters the building with Ann. Ann tells it that they should return to the party, but when it rasps at her and she queries who it is, it grabs her by the wrist and will not let her go. Ann screams for help and a butler rushes to her assistance. The Harlequin grabs him by the throat and starts to throttle and kill him, causing Ann to faint as the Harlequin lurches over her prostrate body…
The Doctor returns to the secret room and finds, to his surprise, Lady Cranleigh and the Indian, who she introduces as Latoni — an old friend from Brazil. The Doctor informs them that he has found a dead body and when he shows it to her, she identifies it as one of the servants. She requests that he does not alarm the other guests by informing them. The figure is seen returning the Harlequin costume to the Doctor's room. It goes to a room where Ann is lying, and a hideously deformed face is revealed. Ann awakes and seeing the figure flees outside the room where Lady Cranleigh and Latoni are waiting. Latoni enters the room and gathering some rope advances on the deformed figure.
At the party Adric is berated by Nyssa for eating so much food. The servants inform Lord Cranleigh of events inside the house. He finds the body of the dead butler, and Ann's discarded mask. The Doctor arrives now wearing the Harlequin costume, but when Ann also arrives, she points him out as the man who attacked her. Ann implores Sir Robert to arrest the Doctor, and Sir Robert assumes control of events. He asks Lord Cranleigh to tell the remaining guests to go home. The Doctor insists on his innocence, and suggests that someone else has an identical costume. However, as Ann was in charge of the costumes, she knows that there was only one Harlequin. He looks to Lady Cranleigh to provide an alibi but she stays silent. Sir Robert questions the Doctor as to his true identity, which he replies would be rather difficult to explain. He says he is a Time Lord and that he travels in time and space, in a time machine, like that from the works of H. G. Wells. Again looking to Lady Cranleigh he mentions the other body, but she denies seeing it.
Showing Sir Robert the cupboard, the body has vanished and has been replaced by a doll. Lord Cranleigh receives a telephone call from his friend "Smutty" Thomas who he thinks sent the Doctor to the cricket game, and he realises it is not the right man. Lord Cranleigh informs Sir Robert that the Doctor is an impostor, and that the real doctor missed his train. The Doctor is arrested on suspicion of murder, and his companions are accused of being accessories. They are driven off to the police station. The Doctor asks the police sergeant to divert to the railway station to show Sir Robert the TARDIS, but to his dismay it is no longer on the platform. However, when they arrive at the police station, they find that the TARDIS has been brought there.
Back at the house Lady Cranleigh tells Lord Cranleigh about the other body, that of Digby the servant. Realising that the Doctor must be innocent, he argues with her. When Ann approaches them he informs her that there is something she must know. In the secret room, the bound figure once again slips his ropes, and attacks and kills Latoni, but not before he hides the room key between the floor boards. Not able to find the key, the figure starts stuffing newspapers under the door, and then sets them on fire.
The Doctor unlocks the TARDIS and allows Sir Robert and the police sergeant to enter. Sir Robert is astounded by what he sees and offers the Doctor an apology, but he is still concerned about the murder. Lord Cranleigh telephones the police station and informs them of the second body. The Doctor uses the TARDIS to get them all back to Cranleigh Hall as quickly as possible. After furiously denouncing her parents, Ann runs out of the house and throws her arms around Sir Robert. The secret room is now ablaze with the fire started by the deformed figure, who breaks out, and goes to the main hall where Lord and Lady Cranleigh are talking. He backs away from them, but the Doctor's group arrive from behind. The figure grabs hold of Nyssa and throttling her, drags her upstairs. The Doctor cannot follow him due to the fire which has now spread to the corridors. Sir Robert demands to know what the deformed figure is, and Lady Cranleigh reveals that it is her eldest son George, which the Doctor had already worked out from seeing the Black Orchid and Latoni. She insists that George would not harm Ann, but the Doctor points out that he has the wrong girl.
Running outside, they see George carrying Nyssa out onto the roof. The Doctor asks Lord Cranleigh to hold George's attention, whilst he tries to find a way through the house to their position. Lady Cranleigh confesses the truth to Sir Robert: George's hideous injuries were caused by the Kojabe Indians, who also cut out his tongue because they held the Black Orchid sacred. Losing his mind, he was rescued by another tribe of Indians, of which Latoni was a member. She admits that George killed Digby. Lord Cranleigh climbs onto the roof to confront George, and the Doctor has also reached the roof. The Doctor implores him to release Nyssa, telling him to look down and see Ann on the ground. Seeing it to be true, he releases Nyssa. Charles approaches his brother to thank him. George recoils, but he is too close to the edge. He trips and falls, and is killed.
After the funeral, the Doctor departs. Ann has given Tegan and Nyssa their costumes as a present, and Lady Cranleigh presents the Doctor with a copy of George's book: Black Orchid.
Doctor Peter Davison (Fifth Doctor)
Companions Matthew Waterhouse (Adric)
Sarah Sutton (Nyssa)
Janet Fielding (Tegan Jovanka)
Michael Cochrane — Lord Cranleigh
Barbara Murray — Lady Cranleigh
Gareth Milne — The Unknown/George Cranleigh
Moray Watson — Sir Robert Muir
Ivor Salter — Sergeant Markham
Andrew Tourell — Constable Cummings
Ahmed Khalil — Latoni
Brian Hawksley — Brewster
Timothy Block — Tanner
Writer Terence Dudley
Director Ron Jones
Script editor Eric Saward
Producer John Nathan-Turner
Executive producer(s) None
Production code 6A
Series Season 19
Length 2 episodes, 25 minutes each
Originally broadcast March 1–March 2, 1982