On this week's Thursday night horror movie — OK, it was an episode of Grey's Anatomy, but with all the creepy music and quick camera angles and ghosts, didn't it feel a little like a horror movie? — a lot of our continuing plotlines come to their conclusions, with Meredith dealing with the serial killer and Izzie calling out Denny for sticking around. There's a little comic relief with Lexie and Mark, but most of the episode is pretty heavy. Ready to chat? Just read more.

Finally. Finally, finally, finally, Izzie Stevens realizes that seeing her dead ex-fiancé — and kissing him, and having sex with him, and talking to him in public places even though nobody else can see him — is not OK. Finally, Izzie knows something's wrong with her. And it scares her, of course, to know that she's sick, but it doesn't seem as scary as the possibility that Denny's just going to be around forever, creepily saying "I'm here for you." Of course, it took Izzie a ridiculously long time to wise up and act like a scientist (or like the doctor she supposedly is) to even think that maybe it was an illness causing her to see and hear Denny all the time. Even in this episode, she suggests that maybe the crazy part of her was the part that thought Denny was dead in the first place. Regardless, it's finally happened: Seeing Izzie again may be Denny's heaven, but it would be Izzie's hell, and she's not done living yet. It's not like we actually see her tell anyone she's sick; I figure that'll be strung out a while longer. But at least there's some kind of explanation of what's been going on.

Meanwhile, the resolution to the serial killer story is actually a lot more complex than what I was predicting last week, when it seemed certain that Jackson would get the killer's organs. It does look for much of this episode like that's how things will end, with Meredith content to let William die and Bailey knowing that's wrong but letting her love for Jackson to get in the way. The twist that William was just playing Meredith so he'd have a friendly face at his execution seemed bizarre, but that aside, I liked the big moments here: Derek saying it's up to Bailey to decide whether he's a surgeon or an executioner; Jackson opening his eyes when it seemed all hope was lost.

The execution scene itself is hard to watch, but it does take care of another problem: the Meredith/Cristina fight. When Mere is at her lowest, there's only one person who can help, and Derek will never be able to fill in. When she's inconsolable, she needs Cristina, and I'm glad that Cristina could put their rift behind her and step in for comfort.

Meanwhile:

  • Lexie breaks Mark's, er, "bone." 'Scuse me, what? I guess it provides both our comic relief for the evening and our "Oh, Mark can be kind of a sensitive guy sometimes" moment, and it did crack me up when Lexie volunteers to stroke his hair and he looks at her with crazy eyes, but it mostly feels out of step with the rest of the episode.
  • Nice that Lexie and Sadie are still friends, even though it does require thinking about Sadie's "Twist and Shout move."
  • Owen admits to Cristina that he's got a lot of issues to work through, but she wants to date him anyway. They're one screwed-up couple, but I like that they know it.
  • George O'Malley had what, three lines?
  • Did the Denny narration catch anyone else off-guard? At first I wasn't sure if it was Denny or Alex.

Your thoughts? Glad that Izzie's had an epiphany about her illness, or dreading what comes next? Pleased with how the serial killer story wrapped up? Freaked out that what happened to Mark can apparently actually happen? Sound off below!

Photos copyright 2009 ABC, Inc.