Ambrose Burt is a non-canonical character created for ITV's 2006 adaptation of the novel The Sittaford Mystery. He is an associate of an American visitor to Exhampton, Martin Zimmerman. They are seen checking into the The Three Crowns hotel early in the show. Ambrose Burt is portrayed by Paul Kaye.
Through the course of events, various scenes show him involved in suspicious activities with Zimmerman. He gives Zimmerman various injections. Later we also see Zimmerman suspiciously sending Burt out with a coil of wire and sending him out to do something.
These actions are only explained towards the end of the show. Burt explained Emily Trefusis and others investigating the death of Clive Trevelyan at first that he is Zimmerman's personal physician. He had refused on principle to join the N.H.S. and had to find employment somehow and Zimmerman was wealthy enough to hire him. Later he admitted that he had been struck off the medical register. The injections and capsules which he gave Zimmerman were not drugs as Emily and the others Trevelyan supposed. Burt explained that they are simply coloured water. He gave them to Zimmerman because they kept him happy and he paid good money for them.
As for the coil of wire, it turns out that it is nothing more than a radio antenna. Zimmerman is a fan of American football and, on the night of the murder, wanted to listen to a certain game being broadcast from California. As the reception was no good, he sent Burt to the roof with an antenna to improve the signal. Earlier on he had told the investigators that he had been on the roof stargazing.
While on the roof, he saw what he correctly supposed to be Trevelyan's killer approaching the hotel. Burt tried to blackmail him but he was killed. Burt's body was then placed in the larder. James Pearson, also locked up in the larder on suspicion of killing Trevelyan, woke up from a drunken stupor to find a blood-soaked knife in his hands.