There's a killer coming to Seattle Grace. E! Online spoke exclusively with Eric Stoltz about his upcoming three-episode guest starring role on Grey's Anatomy, and what he says about his death-row inmate character sounds downright ominous.

Eric teases about the purpose of his character, which debuts tomorrow in "Wish You Were Here" (follow link for some quality sneak previews): "I would have to say that I insinuate myself in between Mer and Der in a way that isn't exactly helpful."

Hmm. What do you suppose that could mean?

Says Eric (with a fair amount of feigned affrontery), "I'm not about to tell you what happens! Why would anyone do that? I wouldn't want to know what happens!"

Seriously though, who is this fellow, and how does he impact the delicate fabric of relationships - professional and otherwise - at Seattle Grace? As Stoltz tells it:

"My character's name is William Dunn, and he's a death-row inmate who came to Seattle Grace due to the fact that he has a shiv shoved in his back during a fight in the prison yard."

"The nature of his crime is actually revealed in the episode of show that airs on Thursday night, so I would hate to give it away right now."

Shonda Rhimes invited Eric to appear in front of the camera after his second directorial outing on the show. But the opportunity wasn't what he expected. He says:

"My ego took over, and I thought [the part] was a romantic hero, someone to come and save the day. When Shonda told me it was a death-row inmate, I was a little bit stunned."

Shonda convinced Stoltz it was still an intriguing part.

"She was saying how most people who do truly evil things usually are not evil 24 hours a day. They have friends, they have a life. You should really hate this man for all that he does, but because that part is so well-written, that character gradually works itself into your subconscious, and some deep, disturbing recognition happens."

As for the rest of the transition from director to actor, it was a little... rocky. As Eric tells it: "The cast had some fun at my expense when they realized I was no longer directing and I was merely acting, handcuffed to a bed. Some of them took advantage of that and sadly, in a cast filled with attractive and talented women, I think the person who took the most advantage of my position was Patrick Dempsey. More than once, that man gave me noogies and tickled my feet."

Tickle attack by Patrick Dempsey? Could be worse.

Steve Marsi is the Managing Editor of TV Fanatic. Follow him on Google+ or email him here.