A six-year-old girl critically injured (and subsequently dies) in an apparent robbery gone bad tests positive for a sexually transmitted disease, putting the detectives on the trail of the family, then the store clerk, and the son of a prominent attorney who had appeared to foil the crime. When evidence turns up that the little girl's older sister was dating the alleged sexual predator, Cabot has to work some legal magic to eradicate the deal made with the older sister for testimony.