Internal affairs looks into whether Jinny followed police procedure in an incident in which she shot the man who killed her brother (in the season 3 finale). Raina must testify about her part in the incident and is faced with a serious decision. Nate and Raina look into a suspect's hunger for sex possibly linked with a murder.

Raina tries to why D.J. a baseball player is accused of Rape, but Raina is almost taken off the case because Johnny (Raina's Boyfriend is a friend of the baseball player. Magda gets a surprise from Gabe a divorce. Now they must figure out to tell Ben.

The inspectors look into the mysterious kidnapping of a young lady named Melissa and wonder if the kidnapping is real. Raina questions Tom about the disappearance of his stepdaughter Melissa leaving Nate and Raina to wonder if Tom is telling the truth.

Magda tries to figure out if she did anything wrong the night her husband returned home from a music tour. Jinny tries to get Magda to understand what she would do if the situation were reversed (if her husband had an affair)

The disappearance of Melissa starts to get really strange when Melissa arrives at the San Francisco police department giving everyone there a big shock. The inspectors also learn that Melissa's father is a sexual predator.

Kate learns that a coma victim has awakened after nine years. Kate hopes to solve the case with the help of the victim. Also Regan learns that her son David was accused of stalking someone and is also schizophrenic. Now Reagan asks Kate if she can look at the files.

Stacey Reynolds tries to help Emma Weber to reconnect with her family she is worried that her son won't remember her after nine years. Emma identifies the person who killed her husband Evan nine years ago from a picture in the newspaper.

Kate, Raina, Nate, Magda, and Jinny must find a way to get Stacy, the principal, and 10 students out of the school safe and sound when they're held hostage by armed terrorists. The team meanwhile must figure out who these people are and why they're doing this. Also, Jinny and Hank get married.