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.

CD and Nate find out if a woman was raped by her best friend's boy Friend; Kate wonders if her relationship with Louis will continue.

When Magda and Peter bust a meth lab, Magda gets an unpleasant surprise. Jinny goes undercover to bring down the owner of a strip club who forces dancers to have sex with celebrity customers. CD and Angela investigate the death of an homeless man and try to figure out how he got to the streets . Kate is having a relationship with a younger man, the assistant district attorney.

The inspectors try to figure out why a high school student was shot. The principal of her school doesn't believe that it is a serious problem. Later, a car is set on fire in the school parking lot. Jinny talks with Hank about having their wedding held at her father's home and trys to convince him to let Casey and his partner get married there as well. The detectives discover a cryptic website with horrific threats that will keep you in suspense until part two of this two parter.

The inspectors look into the murder of a pregnant woman and wonder if her husband could be connected in the murder. The inspectors learn that he was rock climbing alone at the time of the murder. Later, new suspects keep popping up and in a shocking ending that will leave you speechless, the murderer is revealed.

Stacy is ready to try and become a full-fledged police officer and leave her job as police services aid. Todd is angry because Stacy didn't tell him of her decision first. The inspectors aren't sure if they are in a gang war when a gang member is murdered. They question a reporter who arrived at the crime scene before police did. Stacy, meanwhile, is shocked when she learns that her parents are coming to see her and that Todd is trying to heal the relationship between her parents and Stacy. Stacy hasn't spoken to her parents since she left home a few years ago. Stacy's parents think she will marry Todd and are shocked at the announcement she makes at dinner.

The detectives look into a district attorney's past to learn why he was brutally murdered. They soon learn he had HIV and may have exposed virtually hundreds of people. Kate is concerned that Katie Ann isn't walking soon enough. Stacy has to serve 39 subpoenas and encounters a dangerous situation when delivering one. Jinny returns to work after becoming a new mom and learns that Kate isn't immune to being a nervous grandmother just as Jenny feels nervous about being a first time mother and having to let everybody touch her baby.

Raina and the missing woman are trapped together in the small basement with no apparent way out. Kate, Nate, Stacy, and Magda meanwhile are shocked to learn the surprising identity of the kidnapper and are extremely worried when they learn that Raina has gone missing.

The Division is on the hunt for a serial killer who left a body in a local landfill. Another missing woman supposedly left a message on her computer that read ""I am okay"". Stacy gets a surprise visit from her former fiance and tries to explain why she left him at the altar. The missing woman's therapist tells Kate that she believes one of her patients may have had something to do with the disappearance of her. Raina meets Johnny's former girlfriend who asks that Raina stop dating Johnny so she can go back to dating him.

Reagan continues to find evidence to prove her son's innocence. When Reagan and Kate try to interview him in prison they don't get much information out of David as to whether he killed Mary O' Reilly. Stacey is asked to help her friend track down his missing sisters. Stacey learns that the missing sisters came from Chechnya . After the sisters of Stacey's friend are located in a truck inside the truck four bodies are found dead due to dehydration. Stacey 's friend is asked to see if he is sister Katrina is one of the bodies in the truck. Miquel tells Magda that Katrina is still missing. Reagan goes to visit David who questions whether he killed Mary and wonders what might happen if he is convicted of the murder.

The Division investigates the murder of Sara Allen who was looking for her daughter. At the scene a note was found telling Sarah's daughter that she was a bad mom but was still looking for her daughter. Magda meets "" a floating inspector "" named Regan (who is filling in for Jinny who is on maternity leave) Magda doesn't like Regan and soon learns that the inspector has a lot of questions to answer. As Magda and Regan look into the murder of Sara Allen Regan is looking at footage of a news report and soon sees a suspect on screen. Kate asks Magda to go undercover at a foster care agency to look for the daughter of Sara Allen only to discover that several children are missing. Reagan does some investigating of her own while serving as a guard for Magda. She carries with her a picture of David (the person she saw on the news report)

The investigators try to figure out how a small time drug dealer was killed and why. The division learns that Jennifer Davis knew Ray Turner when she was in Las Vegas. Magda tries to learn if Ray was ever abusive to her. Nate tries unsuccessfully to end an affair with Suzanne because he knows her husband is a cop. Stacey learns Mr. Hicks paid a lot of money to mess up a DNA test because he found out that Jennifer Davis isn't the biological daughter of Joe Davis.

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.

The daughter of a wealthy family is investigated by police who want to understand how members of the Hayes died in the car bomb and who exactly had motive to do it. Florence Hayes filed papers about a month ago that listed three of Florence's a daughter's joined into split the will worth 80 million dollars. Magda also discovered that Jack was taken out of the will because he may have been involved with the plotting to set off the pipe bomb.

Jinny tells Kate that she is pregnant and is told to stay off the streets and work behind a desk Jinny is unhappy with the policy regarding police officers that are pregnant and wishes she could be on the streets until she goes on maternity leave. Now she has to tell hank that he is about to be a father. Jinny tells hank that he will be a father but as he learns this news from jinny Nate eavesdrops on the conversation between Jinny and Hank while he is waiting to ask a favor of Jinny . Nate asks Jinny to supervise a search while he goes and speaks with the District Attorney. Lisa learns that her husband is a rested for selling drugs and now must talk to the investigators and try to get her husband's charges reduced.

Diane Evans faces her father in court for abusing her as a child. she is shocked when the Judge in the case releases her father because of a Califoronia law that was enacted in 1993. The Judge releases Cale Gillman because the crime was committed before the law was enforced. Diane Evans is angry that the case against her father is dropped now the captain gets word that Diane Evans 's father Cale Gillman was murdered Jinny and Mageda begin to suspect Diane may have killed her father because he didn't go to jail for his crime.

Stacy Newland helps Jinny & Magda figure out happened in a nightclub. The Medical Examiner tells Raina & Jinny something interesting about the body. The parents of Lee Anne are told she was she shot after believing she died in the nightclub fire. The Medical Examiner tells Jinny & Magda that their shooter was a man not a woman.

Jinny has to figure out how to tell Jack she is in love with Hank. The Division tries to find out why two gay men were attacked at an AIDS Benefit. Kate tells Sally that Nick may helped attack the two men because his friends did but Sally wants to have the case tried as a hate crime. Kate tells Sally the two men were watching the concert peacefully. Kate talks with a suspect who remembers seeing to girls get angry because their parking spot was taken.

Nate and Raina look into the Suicide of Tom Burke who worked at the same facility that Irene (Nate's sister lives. Irene believes Tom was murdered. While Nate questions Bob about Tom Burke and weather Tom took his medicine they find out Bob did not't give out medication. Raina & Nate wonder how Tom got his medicine.

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.

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.

Jinny & Magda are trying to find burglar Grant coal train but they must deal with a bounty hunter who is also looking for the burglar. The methods used by the bounty hunter drive Jinny & Magda crazy. Kate fights to keep her Granddaughter from the surrogate mom that wants to adopt her.

In this episode Nate gets Raina as a partner because CD dumped him. Jinny tells Magda that she got divorce papers from Jack. Raina tries to find out why CD left. Kate considers hiring Stacy Newland to help Kate. Amy whose husband hit her is killed by ""Buzz"" their pit bull was going to be trained as a guard dog. Jinny meets Hank Riley a sketch artist but doesn't seem ready for love.

Jinny vows to avenge her brother's murder. Kate pays a visit to The Division and has mixed feelings about a new boss taking over. CD tells Nate her fears of almost losing him after he nearly got shot. CD & Nate go to a bar to meet a suspect but end up in a shootout. Raina thinks about dating Johnny. Magda ends her affair with Jonah. Jinny into Ray the man who killed her brother. Kate thinks about leaving her job until she finds out that the new boss is planning to fire Jinny. In a season-ending cliffhanger, one of The Division is shot.

Jinny learns that Jack will move, the team watches a crime about to happen. Kate begins her recovery. Magda tells Jonah she might be having a baby, Jonah isn't ready for kids. Kate comes home from the hospital CD & Nate try to catch prisoners who escape custody hurting Nate. Jinnny & Magda talk about if she will have a baby while waiting for Gina Bracken. None of the team likes the new captain because he wants everything done by the book. Gabe is disappointed that she isn't pregnant. Kate asks to be updated on things, she can't get used to having a stroke. Jinny leans that the gun that was used to kill a Marshal also killed her brother John.

Jinny & Raina into the deaths of two lovers, the parents of the kids now deal with the news. Magda must decide how handle her relationship with Jonah before Gabe comes back. The crime goes from suicide to murder suicide. Mrs. Johnson is told her son Rob, may have shot Tara because someone tried to get away. Magda wonders if she is pregnant with Jonah's baby, Jinny believes she isn't. Lilly wants to plan a party for Nate, but finds out he loves CD.

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.

CD & Nate look into the case of a woman who may have left her baby daughter behind. Will Jinny leave AA for good?

While handling a hostage situation, CD meets her new partner, Angela. While trying to figure out who murdered a famous psychiatrist, both also need to take shooting tests. Magda and Peter, acting on a tip, discover illegal Asian immigrants who are being forced to work in exchange for their being brought to America. Kate is dismayed when Jinny makes a mistake while trying to bust deadbeat dads and even more dismayed when her 18-year-old daughter, Amanda, announces her engagement to her slacker boyfriend.

Candace (C.D.) and Angela disagree over how to investigate a female murder victim; Jinny thinks she is being punished when she is assigned to a case involving a murdered dog.

Jinny learns her brother a cop died. Also CD & Nate look into the case of a psychiatrist who may have raped a patient with MPD (Multiple Personality Disorder) The psychiatrist says ""Liz"" is highly charged but says he didn't rape Christine. CD & Nate ask about Jinny who misses her brother. Jinny tells Jack her brother's locker will be cleaned out. Jack thinks Jinny is on drugs. Magda wonders if the relationship with Jonah should continue. Magda realizes her affair with Jonah is going to far. The funeral of John Exstead Jr. leaves Jinny in a blanket of memories.

In this episode the whole division is trying to find a baby that was in the backseat of a car during a hijacking.

Kate spearheads an investigation of two officers who shoot and kill an unarmed man; Jinny's drinking problem causes her to miss a meeting with a star witness.

Angela looks into the death of a reporter.

Jinny Looks into the case of woman who was raped.

Magda and Jinny's investigation into the death of a college student exposes the rampant homophobia in the victim's fraternity. The case touches a nerve with Jinny, whose own brother's coming-out unleashes a fury of prejudice in her family. CD and Angela look into a case of alleged elder abuse and a shocking development causes them to question their earlier decisions. Angela learns of CD's marital woes. Kate and her younger boyfriend fight about the state of their relationship, which she wishes to keep secret.

While at a gun show peter & Magda find out that a dealer sells weapons.

Kate reopens her first-ever homicide case when it is revealed that the wrong man may have been convicted. How will she handle the ramifications of past decisions? Jinny and Magda investigate the baffling murder of an Asian man. CD's problems with her husband's infidelities come to a head.

Jinny is the target of a seemingly random shooting. The efforts of her brothers and boyfriend to make her feel safe do little to alleviate her feelings of vulnerability. CD and Angela investigate the murder of a pizza deliveryman. Magda struggles to resolve her conflicts with Peter.

Kate deals with heated community conflict surrounding an upcoming murder trial, as the entire squad pitches in to interview reluctant witnesses. The gun used to kill CD's former partner is discovered, dredging up painful memories. Jinny's boyfriend wants to take their relationship to a new level. Magda voices concerns about Jinny's drinking. Angela gives her husband a big surprise.

Magda and Jinny attempt to help a troubled teen take responsibility for her actions. During a stakeout, Angela and C.D. evaluate their partnership. Kate ruffles the feathers of her future son-in-law when she takes charge during her daughter's medical crisis. Will the young couple's relationship weather this storm?

Magda's rejection of a judge's sexual overtures endangers the outcome of a trial in which she is a key witness. Much to C.D.'s consternation, her deceased partner's informant, the only suspect in his death, is brought into custody. Kate and her sister must deal with their mother's deteriorating health together—and face their own troubled relationship.

Magda and Jinny investigate the death of a compulsive gambler. C.D. reveals the truth about her partner's death to Angela, putting their personal and professional relationship to the test. Sparks fly and old wounds reopen when Magda bumps into Ben's estranged father, Gabriel.

Magda goes undercover as a prison inmate during a murder investigation. C.D. and Angela get more than they bargain for when they take a documentary filmmaker on a ride-along to serve a subpoena. When Jinny meets Theodore's family and ex-girlfriend, her drinking problem resurfaces and threatens to destroy the romantic relationship.

C.D. and Angela investigate an attempted murder and discover that the victim is a former teen criminal who achieved celebrity because of her crimes. Jinny makes a surprising decision about going on a weekend trip with Teddy but gets a surprise of her own. When she is offered a deal that could end her investigation, Angela must make a decision that could end her association with The Division and faces pressure from her husband.

Kate suspends Jinny after she shows up to make an arrest drunk and disheveled. Magda, secretly organizes an intervention in the hopes that Jinny will confront her addiction and go to rehab.

Jenny is back from rehab.

Kate works with Jinny and Magda as they investigate a powerful litigator who is suspected of killing a missing intern. However, the intern eventually reveals herself, alive and well, having planned the entire charade in order to bring down the womanizing politician. Nate and C.D. find out that thousands of dollars were stolen by a man who took the money to pay for his disabled son's medical bills.

Jenny Looks into a murder.

Jinny and Magda try to solve the murder of a suburban mother who was going through a difficult divorce and fighting to get her toddler into an exclusive kindergarden. C.D. and Nate investigate the murder of an evil stalker. Kate's daughter returns for a visit and has several surprises in store.

Help is needed to find a missing girl.

A serial killer is homless woman herself.