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 Captain John Hart with talk of golf, while the Master (disguised as a naval officer) 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 by telephone but was unable to get through to the Minister. When the Sea Devils attacked the prison, Trenchard fought back with his old service revolver but was killed after he shot dead two Sea Devils. (TV: The Sea Devils)
Behind the scenes
- In Malcolm Hulke's novelisation of the story, Trenchard does not shoot two Sea Devils as shown in the televised version, but instead is killed without firing a single shot after he forgets to take off his revolver's safety catch. When the Third Doctor, Jo Grant and Captain Hart later find Trenchard's body, the Doctor notices the safety catch is still on and resets the gun when Jo and Hart aren't looking — thus ensuring no-one will find out Trenchard died a failure.