Hi, Renate,
Yes, I was confused about why Leslie Vickerage was replaced until I read Nat's comment that she became a Mum

and that's why she left the series. I thought she, as an actress, had really beautiful brown sparkly eyes and had great kissing scenes with Nat as an actor. I loved the way they played the "room service" scene together in "Finding Joseph".
I still just don't see Helen's character arc moving from "Payment in Blood" through to impulsively agreeing to marry Tommy in -- oh shoot! --- I can't remember, was it "In the Presence of the Enemy"? You know, the one where he practically pins her against the wall and says something to the effect of: "Let's get married this weekend!"
(And I'd be lying through my teeth if I said that this scene didn't make me swoon!

*le sigh*)
Another aside, Tommy is so gorgeous and yummy, he's also so physical (remember how he gently brushes Bobbi's hair back from her face in "A Great Deliverance") and obviously caring -- I mean, sheesh! Why isn't Helen swept off her feet?
I wonder this especially since they were supposedly old friends according to the pilot. So she knew him, she knew he wasn't a blackguard who would "love 'em and leave 'em". Once again, I want to stress that I'm not criticizing Leslie Vickerage as an actress, I'm speaking of the character arc of Helen, the character, whom I find an enigma.
She just seems so unloving towards him.
And speaking of unloving, how about poor Tommy Lynley who gets ripped to shreds by the two most prominent women in his life within ten minutes of each other in "Finding Joseph": Helen in her rebuff to him, and Havers in her furious outrage over him having painted her ratty old apartment.
Sheesh! If I had a man who decorated my apartment, and paid for it, I'd give him a big hug, even if it is "duck white".