[spoilers] Which character had the best introduction?

[Silktie]

Adam's worked the best for me to date (although I haven't seen season 7 yet so cannot comment on Lucas' introduction). I think Adam's introduction fitted well into the storyline of the stand-off between Tom and Harry, and he was different enough as a character from Tom to satisfy me. After a season and a half of enduring Tom as a tortured soul, Adam was a breath of fresh air as someone who actually looked like he enjoyed working for MI5, and thought it was worthwhile!