In the novel Evil Under the Sun, Inspector Colgate was the officer of the Devon police in charge of the investigations into the murder of Arlena Marshall on Smugglers' Island. He worked under the chief constable Colonel Weston and also with Poirot who was at the time a guest at the Jolly Roger Hotel.
In the course of the investigations, Colgate also traveled to London to consult with Scotland Yard, with the solicitors of Arlena Marshall, and also to Surrey to consult with the police at Blackridge. Poirot liked Colgate, who came across as professional and imaginative. He "liked his rugged face, his shrewd eyes, and his slow unhurried manner". Colgate did not express surprise when Poirot asked for unusual items such as a list of unsolved cases of strangulation over the last three years. He got the information and quickly saw the connection.