Billy and Jase (Stephen Lord) go face-to-face with gangsters in dramatic scenes to be broadcast next week. After their plans go horribly wrong, Billy must face the wrath of his loyal wife Honey, played by Emma Barton.
"I'm lucky that my boss gives me some pretty great storylines!" Fenwick told Hot TV magazine. "I like the fact that just when you think you've got Billy figured out, he'll do something that will totally surprise you!"
He added: "Billy has always had this dark side to him, it's only recently that he has become a family man and that's down to Honey. Even though he's the runt in the Mitchell litter, he's always had this huge chip on his shoulder which I think makes him more dangerous than Phil or Grant."
Though the actor is sticking with the BBC One soap, Barton filmed her final scenes last month after being axed by producers.
Speaking about the decision recently, Fenwick admitted: "It's gutting for Billy and for me. I'll really miss Emma. Don't get me wrong, I'm happy where I am but I do wonder what's next for my character."