After making fans wait nearly a month for a new episode, the writers of "Grey's Anatomy" supplied some juicy moments in this week's offering. (Spoiler alert: Stop reading now if you've saved this episode for later viewing.)

The big news was that the daughter Izzie gave up for adoption 11 years ago has leukemia and needs a bone marrow transplant. Izzie agreed to be the donor, but she was heartbroken when her daughter refused to meet her.

Katherine Heigl's performance as Izzie was lovely and more restrained than anything she's done on the show lately. It was as though the annoying Izzie of this season had been replaced, at least temporarily, with the appealing Izzie of seasons one and two.

Meanwhile, George tried to ignore Izzie in the wake of their unplanned hookup, but he couldn't stay away. He held her hand through the bone marrow extraction, even though it meant missing a coffee date with Callie. When Callie questioned him, George did his best to lie about where he'd been. But Callie's no fool: She can tell when her husband is hiding something.

As interesting as the Izzie-George-Callie story line got this week, another plot twist may prove even more compelling: Is Derek really going to dump Meredith?

Meredith began the hour balking at the attention she's been getting from her stepmother, Susan. "I think I scared off my fake mommy forever," Meredith told Derek after barking at Susan to go away. But Meredith later softened when Susan made a plea for closeness.

Trouble is, Meredith may be gaining a family just as she's losing her boyfriend.

An exhausted-looking Derek (it must be easy for Patrick Dempsey to look this tired with newborn twins at home) was furious after discovering Dr. Webber isn't naming him chief of surgery because he wants to protect Meredith's happiness. Derek ended the episode alone in his trailer, ignoring Meredith's phone calls and wondering if their relationship is too much of a liability.

More bad news: A couple arrived claiming to be Jane Doe's parents and she was thrilled. But Alex, who's grown increasingly close to her, was stuck with the painful task of telling her the couple realized they were mistaken. She was deeply upset and took out her anger on Alex.

Colin Marlow decided to leave Seattle Grace after competing unsuccessfully with Burke for Cristina's attention. His parting words were bitter, and he left Cristina wondering whether she's changed for the better or worse in the years since she dated him.

This heavy episode's much-needed comic relief was supplied by Mark Sloan, who found a new strategy in his pursuit of the chief of surgery job: After witnessing the Chief's feeble attempt at flirting with a woman, Sloan volunteered to be his "wingman." But Sloan may get more than he bargained for: Rather than meeting a stranger at Joe's bar, the Chief ended up dancing with Addison.