It's Halloween at Seattle Grace and the newly formed resident management team of Callie and Miranda instruct the residents to watch out for weirdos, especially injuries related to the annual chainsaw pumpkin-carving contest. Callie tells Izzie to address her questions to Miranda and when she asks why, Callie announces to everyone that it's because Izzie's been sleeping with her husband.
Meredith is surprised but supportive of the new couple while Cristina huffs in disgust when they say they're waiting to be together "out of respect for Callie." When Mark hears that Callie is free, he offers to comfort her, day or night, especially night, but she declines.
Ava is disappointed that Alex didn't come for her, so she shows up at the hospital, for him and they fall into bed together. He ignores a page from his intern, Norman, to stay with her.
A well-dressed man comes in, claiming that his left foot doesn't belong to him, and asks Miranda to amputate it. Instead, she gets him a psych evaluation and some anti-anxiety medicine. But another patient, who cut off his finger carving a pumpkin, conveniently leaves his chainsaw unattended and the would-be amputee uses it to try to cut off his own foot. Callie has no choice but to finish up the job for him.
A patient in need of a heart transplant faces a terrible dilemma when his daughter is killed and her heart is a perfect match. He tells them to give it to someone else, but Dr. Hahn has already been called in to perform the transplant. Cristina is eager to offer her services, but Dr. Hahn says she doesn't approve of Cristina's m.o. of sleeping with her mentors and chooses Izzie to assist her instead. Dr. Hahn tries to convince the man one more time to take his daughter's heart, but he refuses, saying it would haunt him everyday if he did. George speaks up and says that if he could have, he would have given his father his heart, and the man agrees.
Izzie confronts Cristina for judging her for sleeping with a married man, accusing her of doing the exact same thing by sleeping with Burke. When Cristina says it's different because George was married, Izzie points out that Meredith also slept with a married man but Cristina doesn't care about that. She claims she would have defended Cristina to Dr. Hahn, if asked and tells Cristina to cut her some slack.
Derek pays a boy to tell Mark he's his father. After the joke is over, the boy reveals why he's really looking for Mark: He was born without ears and he wants the plastic surgeon to construct them for him, pro bono. Mark says he can volunteer his services, but he can't ask any of the doctors or nurses to help as he's got no "social capital" at the hospital. The nurses have even formed an anti-Mark club once they realized he was using the same pick-up lines on all of them! Meredith convinces everyone to help out, by "trick or treating" with the boy, to show that every day is Halloween for a boy with no ears, until he gets the surgery. Miranda even blows off her first Halloween with her son to perform the surgery, which doesn't go over well with her husband.
Mark is impressed that Meredith was able to round up all the necessary surgeons and a free OR and when she confesses that it was her first time trick-or-treating since her mother never made time for it, Mark looks at her in amazement and says, "The apple fell far from the tree, didn't it?"
Adele is divorcing Richard, so he asks Cristina if Burke's apartment is free and she tells him it is.
Cristina chews out Dr. Hahn for her "inappropriate" and "unprofessional" comments and insists she did not sleep her way to the top. Dr. Hahn laughs and says, "This is going to be so much fun." Richard announces that she has just agreed to be the new head of thoracic surgery. Cristina declares that she's taking back the apartment.
During surgery, while Callie and Cristina bond over their doomed love lives, Norman collapses. He'd been feeling bad all day and wanted to go home but Alex shamed him into staying and now he's had a stroke. Alex finally answers his page and promises Ava he'll be right back. When Norman comes to, he tells Alex that there was a little voice in his head urging him to choose surgery, even though he's over 60 and blood makes him squeamish. He decides that voice was his late wife, who wanted to make sure he'd be surrounded by world-class surgeons when he had his stroke. He says he's giving up surgery and switching to psychiatry and declares that all the surgeons could use a good shrink! When Alex goes looking for Ava, he finds just her shirt.
All the nurses start flirting with Derek and Mark confesses that he spread the word he was "looking" as payback for the stunt with the boy. Derek confides to Richard, who's depressed over his divorce, that he's depressed because he's also going to have to start dating.
Spooked by a dream in which she finds herself talking to her own body in the morgue, Meredith blames the fact that she hasn't put her mother's ashes to rest. She takes the urn out of the back of her closet and puts the ashes in a baggie and takes them to work, which everyone else finds strange. Lexie tells Meredith that when her mother died, she decided to dig up the family cat and bury it with her, since her mother loved it so much and Meredith is touched by the story. Post-surgery the little boy, who saw Meredith with the ashes, tells her how he flushed his goldfish down the toilet, so it would go back to the ocean. Richard finds Meredith rinsing her mother's ashes down the sink in an OR prep room. She says she thinks it's where her mother would want to be and Richard helps her, saying "Ashes to ashes."