Deakin

 was a Colonel in an army. Captain Ruth Matheson came to visit him in Belize. He had lived in an ancient Mayan temple. He had the Samuel Pepys collection. He was infected with something biotechnical. He then placed her in a maze. He wanted to know about how Ruth joined UNIT. He decided to bargain with Ruth for the Terileptil plague by getting her to kill Zoe Heriot. Zoe didn't die and planted a logic bomb to wound Deakin. He came after Zoe and Ruth hoping to get access to the TARDIS. He was killed when the missile landed on the temple. (AUDIO: The Tactics of Defeat)