[spoilers] Lucas. Just Lucas.

[Logsie]

There are many valid points being made here but I, personally, am finding Lucas a bit easier to understand now. What we have to remember is that Lucas is an artificial construct; as Vaughn said, he's not a real person, he was created by John in order for him to turn his back on his wicked past and make a fresh start unencumbered by baggage. I think the only way he was able to do this is to effectively shut down his emotions - he no longer hears music because it is too closely allied to memories. It also casts new light on his comment to Sarah that "I just haven't been able to feel anything for a long time"; Lucas's personal feelings are switched off most of the time. Yet he is still human, he craves human contact, and he needs the idea of "family" to anchor him so he doesn't lapse into psychosis - whether it be a literal family or "colleagues". It explains why he hung onto his memory of Elisabeta for so long and why he was blindsided when he discovered she had moved on and remarried. At that time he still wasn't sure if Harry had accepted him so he had no spiritual home. He told Harry that without MI5 he would never be home, just back in England. It also explains why he tends to jump in feet first when a love affair beckons - good God but that man is needy! However his affair with Sarah was contrived; he was going through the motions, trying to make himself care and it worked up to a point.

Now he is offered the chance of something real and tangible in Maya which he has convinced himself will make everything alright. He can make her fall in love with him all over again, gradually explain his long absence and the fact that he goes by a different name now whilst at the same time living his new controlled life within MI5. It was always a long shot but Lucas needs to believe it is possible. Vaughn threatens everything so there must be a very good reason why he can't just kill him. It is possible that killing him in cold blood purely for reasons of self-interest goes against everything that his Lucas persona stands for so he won't allow himself to do it. I know he let Danielle die but people have a tendency to rationalise their own behaviour when their back is against the wall. He convinced himself that he wasn't responsible for her wounds and that she was probably going to die anyway, so it was better for her to slip away before anyone else came on the scene and heard her ramblings. Murdering Vaughn would be an entirely different thing. He reached for his gun when Malcolm called him "John" but I can't imagine him actually pulling the trigger on one of his oldest friends either.

I am of the opinion that there is a more practical reason why he can't just get rid of Vaughn, though but I just can't figure out what it is. I rewatched all 6 episodes on the weekend looking for the "clues" which we have been told are there pointing to the traitor. I used FFWD through all the "story of the week" bits and studies al the character interactions but now I have to say I suspect EVERYBODY !