Cruz wonders about whether a fellow officer may be aiding the attack as the masked gunmen continue to attack officers in the hospital. Bosco fights for his life after receiving a critical wound.
Cruz tries to help keep Yokas in the clear for the death of Donald Mann but then finds herself under the watchful gaze of a new lieutenant.
Davis babysits a rookie with paternal ties to Internal Affairs. Monroe worries about helping bust a comrade in arms. Carlos starts to believe that the curse of a street looney may actually be real.
Yokas starts work as a detective and is immediately thrust into a case involving a suicide who leaves an explosive present behind. Sully has a hard time with the continued presence of Finney.
Yokas and Miller try to stop a serial killer who targets girls and comes to the station to challenge Miller to find his current victim before she dies. Carlos and Grace find themselves caught on a false call set up by drug addicts.
Yokas and Miller try to get the location of a serial killer's newest target before all the blood drains from her body.
Cruz faces people that she put away when Interal Affairs sends her to jail. Yokas ponders her own fate, knowing the actual trigger person behind the death was herself. Carlos and Levine look in on a suicidal woman.
Cruz tries to uncover the criminal behind an attack on a councilman who refuses to name the culprit. Davis encounters a convict trying to sell him on a truth about the person behind his father's murder.
Davis seeks revenge for the death of his father with Captain Finney who, in confrontation, outs Sasha as Internal Affairs. Yokas looks into the murder of a teen which may have been wrought by her boyfriend or possibly her family even as she confronts her own teenage daughter over custody.
The rest of the watch learn that Monroe has been working for Internal Affairs, putting her at odds with them even as she needs them the most.
Sullivan remembers his early years on the force. Sully and Monroe team up to locate the men responsible for Davis' father's death as Sully seeks out redemption for his involvement and a way to take down Captain Finney.
Sullivan continues his task to take down Finney. Cruz partners up with a federal investigator to look into a diner bombing which is believed to be a terrorist action. Carlos worries about Levine. Yokas pays Bosco a visit.
A radiation contaminated terrorist causes an evacuation of the 55th precinct station. Cruz and her federal partner continue to track down the terrorists. Bosco is released from the hospital. Carlos debates whether he made the right decision with Levine.
Finney gets a cell call from a boy in need of help. His father has taken him after stabbing his mother. Carlos and Levine seek a mutual understanding.
Cruz chases down a gangleader who is more than willing to kill and kidnap to keep people off a murder witness stand. Grace discovers her missing mother as a street junkie. Bosco questions his return to the streets when he has trouble on the firing range and looks to Faith for help. Monroe lets Sully know that she's pregnant when he insists she get an x-ray.
Dr. Connr and Dr. Durant from the N.I.H. team help out those at Third Watch when a thief starts to spread a mysterious disease. Cruz sees a gangmember killed by a teen and believes she knows who is behind the murder. Yokas worries about Bosco.
Cruz wants to take down a gang leader trying to increase his power base with the testimony of a boy. Sully is paired up with the newly returning Bosco. Yokas checks out a vampire cult for their possible association with a teen's disappearance.
Bosco and Monroe respond to the call of a hostage situation when a woman demands a government check. Monroe takes a bullet from Bosco. Cruz is given hard medical news as her condition deteriorates. Davis and Finney go undercover and Davis unknowingly runs across a prostitute. Davis is told that Monroe has lost the baby he didn't even know about.
Cruz's state of mind affects her greatly when she investigates a Santeria group which may be involved in a woman's immolation. Carlos learns too much information from Levine's family. Yokas approaches Bosco about admitting that he isn't working with full vision and shouldn't be on street duty.
A bad day of traffic gets worse when a driver starts to push a family van into Davis and Finney and then shoots the mother and father, setting the boy free.
Yokas works to diffuse a live televised hostage crisis at a television studio. Bosco saves Emily from the leader of a vampire cult. Cruz seeks Marcel's help in bringing in the people responsible for a string of drive-bys, but the deal sours and the officers of the 55th come under fire.
Gang members lay siege to the precinct house and set it aflame. In the confusion, Marcel makes his escape. Cruz takes the fight to Marcel on his turf and ends his reign with a pair of grenades. Carlos proposes to Levine and then seeks Doc's advice on how to have a happy marriage. The officers are sent to new assignments.