A week after a bomb went off at Seattle Grace, the real fireworks are starting to fly.

When Preston returns home to find Cristina rocking out to her iPod and brushing her teeth (standard morning protocol), their relationship is strained yet again when the phone rings and he discovers that she still leases her original apartment.

Izzie, meanwhile, treats a woman with spontaneous and involuntary orgasms. Her exposure to this patient lead her to "feed the beast" and satisfy her own needs with Alex, even after she recently swore that they were just friends and would not do so again.

But primarily, this episode features the surprise arrival of Dr. Mark Sloan -- the infamous Mark who Addison cheated on Derek with -- in the Emerald City. In his first five minutes at the hospital, he hits on Meredith, then receives a knuckle sandwich from Derek.

The tension between the former best friends is palpable, and Mark's presence mysterious. Yet Dr. Webber allows Sloan -- a renowned plastic surgeon -- to assist in a risky surgery to fix a teenage patient with facial tumors that make his face resemble that of a lion.

Despite a strong chance that he will not survive, the likable patient elects to go through with the operation. He dies during surgery, but Dr. Sloan (assisted by Alex) proceeds with the plastic surgery to fulfill the boy's lifelong wish of appearing normal.

It turns out that Mark's purpose in Seattle is to convince Addison to return to New York and continue their relationship. We learn that she stayed with Mark after Derek left for Seattle, and that this may have been more than a fling. Meredith and her female intern counterparts dub the new doctor "McSteamy." Despite his urging, a conflicted Addison does not meet Mark after work to rekindle their affair, as he requests. But this guy isn't going anywhere... yet.

Meredith's delirious mother, believing her to be five years old, tells her about having an affair in the past. After the younger Grey treats a possibly terminal cancer patient intent on sending angry videotapes to all those who wronged, she confronts her father about the affair -- the first time in two decades that the two have even spoken. To Meredith's dismay, he confirms the truth of her mother's words. Intriguingly, we are led to believe (unbeknownst to Meredith) that the man her mother was romantically involved with outside her marriage is Dr. Webber.

After 28 episodes of pining for Meredith, George finally reaches his breaking point. Unable to harbor his feelings any longer, he tries a number of times to get her attention but is always interrupted by something at the hospital. At the episode's literal and emotional climax, he declares his love for her back at their house. Without words, she embraces him, and they appear to melt away into the throes of passion as the screen fades to black.