After young Sean Hamill is stabbed in the back at the schoolyard, detectives are led to Charlie Monaghan, the older boy who had previously gotten into trouble over Hamill, but it isn't long before their attention turns to Monaghan's half-sister Emma Boyd. Hamill had been torturing the little girl for months because she had two mothers. After getting a nice deal for Emma's side, Benson and Stabler are thrown for a loop when Emma's biological grandparents accuse Zoe, who had never legally adopted Emma, of sexually molesting the little girl, and evidence seems to support their claims.
Michael hosts a Christmas party at the office, but somehow manages to decrease the holiday cheer when he changes the arranged secret Santa pairs to a game of "Yankee Swap," where everyone gives their pre-bought presents to a different, random worker. To boost morale, Michael introduces vodka shots while the others compete for an iPod, Jim hopes that his sentimental present, meant for Pam, doesn't end up with Dwight, and Angela becomes enraged about Michael's party changes.