Shortly after the Master arrived, he persuaded Trenchard that "enemy agents" were working against him and the country. These "enemy agents" were also responsible for ships recently sunk in the area. Trenchard willingly helped the Master, going so far as to distract John Hart with talk of golf, while the Master stole various pieces of equipment. Trenchard became panicked when he found out Jo Grant had seen the Master at the base while the Master didn't care. The Master was able to manipulate him because of Trenchard's strong patriotic views.
Following the Master revealing his contact with the Sea Devil Trenchard began to realise he had been manipulated and he began to be suspicious of the Master. Convinced the Master had received a message from the Sea Devils, Trenchard decided to alert the authorities. When the Sea Devils attacked the prison, he was killed after he shot two Sea Devils. (TV: The Sea Devils)