Captain Rupert Cottam was a non-canonical character who appeared in the 2010 Agatha Christie's Marple adaptation of the novel The Pale Horse. Captain Cottam and his wife lived in their own house in Much Deeping, but because of a fire there, had to move to the the Pale Horse Inn while repairs were going on. Cottam has a feud with Mr Venables. The latter wanted to buy over the Cottam's land but Cottam refused to sell. In one scene in the inn, witnessed by Miss Marple, Cottam accused Venables of setting fire to his house.
Later, Cottam is found dead in his bed. At first his death was thought to be due to natural causes. Later, Miss Marple revealed that he had died after drinking a love potion of spanish fly. Cottam was having an affair with Lydia Harsnet, the housekeeper of the Cottams. She had purchased a love potion from Bella Webb. Unknown to all of them, Zachariah Osbourne had poisoned the potion. Cottam had been having an affair with Lydia and died while in bed with her, after just consuming the love potion.
Captain Rupert Cottam is portrayed by Tom Ward. There is a vague parallel between the Cottams and the Despards in that they both have a dog who has ring worm. Miss Marple sees Cottam treating his dog with an ointment. As such ointments commonly contained thallium, this gave Miss Marple an idea how the string of murders in the story had been committed.