What about a Watcher? Perhaps he'd be suspicious of why Gorion brought Imoen to Candlekeep and in his paranoia he'd be in the middle of investigating them when he finds that they're leaving to the Friendly Arm Inn. Of course he'd follow them until he finds that she's a Bhaalspawn, which would lead to him wanting to kill her. But he can't of course and he ends up maybe saving her life at a certain point (he'd have a chance to kill her then, but he wouldn't follow through). Then he'd join the party.
Anyone want to make a character that falls in love with Imoen?
