Tom was serious, focussed and popular with the team he leads. Deeply intelligent and with impeccable instincts, Tom's job was everything to him and always came first. While this made him an excellent Spook, it didn't make him such a perfect boyfriend, as his girlfriend Ellie quickly found out in series 2. If he wasn't out on missions that put his own life in danger, he was back home, putting his family at risk.
Tom's loyalties were called into question when he tried to convince Harry, Zoe and Danny he'd been set-up in an assassination plot. Unable to persuade any of the team of his innocence, Tom felt cornered as Harry threatened to call in back-up. He shot Harry and ran.
Tom eventually managed to prove his innocence. He was exonerated of any wrong-doing and returned to the Service. However, it wasn't to be for long. Tom's moral questioning of his job caused a massive crisis of confidence. He jeopardised an important mission and Harry was forced to de-commission Tom from MI5. His career is now over and he is no longer a Spook.