The TARDIS arrives on Earth, at a railway station called Cranleigh Halt at 3.00 p.m. on 11 June 1925. The Doctor’s party are taken aback to be met by Tanner (Timothy Block), Lord Cranleigh’s chauffeur, and driven to a cricket match. Lord Cranleigh (Michael Cochrane) and his family assume that the Doctor has come from Guy’s Hospital and inform him that there is to be a ball that night in aid of a hospital for sick children. 

Everyone assumes that Nyssa much be a Worcestershire Talbot as she is the spitting image of Ann Talbot (Sarah Sutton/Vanessa Paine), Charles’s fiancé. The ball is to be a masque and the costumes are chosen: Tegan is to be a rose; Nyssa and Ann have identical butterfly costumes; and the Doctor chooses a harlequin outfit. While the Doctor is taking a bath, a stranger enters his room via a secret passage. The Doctor fails to see the stranger but notices the open door to the passage and goes through it. The stranger meanwhile makes off with the harlequin costume. 

At the ball, Nyssa and Ann are having great fun confusing everyone as to their true identities. The only way to tell them apart is that Ann has a mole on her left shoulder. Lady Cranleigh (Barbara Murray) is taken to one side by an Indian named Dittar Latoni (Ahmed Kahlil), who explains that Digby (David Wilde), one of the servants, has gone. They go to investigate, leaving Tegan dancing the Charleston and Adric eating. A character in a harlequin costume appears, entices Ann/Nyssa to dance with him and then approaches her threateningly in the hallway. A footman who tries to intervene is killed. 

The Doctor, meanwhile, has found a dead body – Digby – in a cupboard. He shows it to Lady Cranleigh and Latoni, who have just arrived. The harlequin costume is returned to the Doctor’s room by the stranger, who then goes to another room and puts the unconscious Ann to bed there. 

Ann soon recovers and runs out to Lady Cranleigh. At that moment the Doctor appears on the stairs in the harlequin costume and Ann accuses him of attacking her. The Doctor tries to explain but Lady Cranleigh will not corroborate any of his stories of secret passages and dead bodies. Sir Robert Muir (Moray Watson), the local police chief, arrests the Doctor on suspicion of having killed the footman, James (Derek Hunt). Charles receives a call from a man named ‘Smutty’ who tells him that the replacement cricketer for whom the Doctor has been mistaken actually missed his train. 

On the way to the police station, the Doctor gains Sir Robert’s permission to stop off at the railway station. To his dismay, the TARDIS has gone. Luckily is has just been moved to the police station. There, the Doctor takes Sir Robert, Sergeant Markham (Ivor Salter) and Constable Cummings (Andrew Tourell) inside. 

Back at the Hall, Lady Cranleigh admits all to Charles. She and Latoni have been secretly looking after his brother, George Cranleigh (Gareth Milne), who was presumed dead after apparently failing to return from an expedition he made up the Orinoco river two years earlier in search of the black orchid. He has been hideously scarred – both physically and mentally – by the natives to whom the flower is sacred. 

Latoni is knocked unconscious by George but, by hiding the key between two floorboards, prevents him from escaping from the room in which he is being held. George then starts a fire to burn through the door. The Doctor transports everyone back to the Hall in the TARDIS. There, Nyssa is snatched by George as he escapes from the burning room and taken up onto the roof. Lady Cranleigh explains that the Kajabi Indians disfigured George and cut out his tongue. Latoni was the chief of another tribe who rescued him and brought him home. The Doctor persuades George to let Nyssa go. Charles then steps forward to hug his brother, but George backs away and falls from the roof to his death. 

The Doctor and his companions stay for the funeral, and when they leave they have some souvenirs. Tegan is presented with the rose dress from the ball, and the Doctor is given George Cranleigh’s book The Black Orchid.

_{Synopsis from Doctor Who: The Fifth Doctor Handbook by David J. Howe, Mark Stammers and Stephen James Walker, reprinted with permission; further reproduction is not permitted. Available from Telos}