A high school girl named Caitlin is throwing a party at her apartment for her friends while her dad is away. Caitlin is shocked when her ex-boyfriend Billy shows up with his new girl Alyson. Billy offers his friends some drugs, but the boisterous party turns deadly when the students collapse after taking the drug, which has possibly been tainted. The lone survivor of this mishap is a girl named Alyson, who is saved because Jamie arrives in time to do CPR on her. He was there with his training officer to investigate a noise complaint.
Alyson wakes in the hospital and Danny and his partner Jackie show up to question her. She doesn't know who supplied the drugs, and only knows that Caitlin was the one who threw the party. Caitlin says that Billy got the drugs from someone at school, so Danny and Jackie head for St. Angela's, where they speak with the principal (Father Leo) and the vice principal (Carol Hoffman). Neither official is very helpful, and they mostly want to protect the students' privacy.
Frank calls in a favor with a cardinal in the diocese, who has been a family friend for years. The Church doesn't need yet another hidden scandal so the cardinal contacts Father Leo to allow the police to investigate. Danny searches the lockers and finds drugs in the one belonging to Wayne Foster. Wayne says he just sells the drugs and didn't do anything to poison his stash.
The police discover that the drugs are clean, so Billy must have been a target. The obvious suspect is Caitlin, who would be jealous over her boyfriend's new girlfriend, but she has an alibi. When Alyson is released from the hospital, she goes for a run and is nearly killed by a car which has a St. Angela's bumper sticker.
Danny and Jackie go to the school parking lot the following day, searching for a car which matches the description. And one car has had its bumper sticker freshly peeled off: the one belonging to the vice principal. Carol was the chemistry teacher, and she used her knowledge and access to the chemistry room supply closet to kill Billy and blame Caitlin. She was having an affair with Billy and got jealous when he went with Alyson.