When the charges against Robert Colson, a prominent attorney accused of murdering his former girlfriend, are dismissed at a preliminary hearing, the detectives and patrol officers look for ways to put pressure on Colson's brother and his family to get one of them to flip on him; Andrea takes a personal interest in the story, which keeps David's name on the front page and causes friction with her mother; Joel, who also has taken the case to heart, risks his life as he obtains the evidence that will close the case legitimately after he disagrees with Ray's planting evidence against Colson's sister-in-law to use as leverage.

Teresa's ambulance is hijacked by a thief who threatens to kill her if she doesn't save his brother, who's been shot in the heart during a burglary; Ray and Tom go undercover to track down a trio of larcenous pranksters, who get the scare of a lifetime when they're captured; David has a horrifying time at a Hollywood Halloween party when Andrea breaks off their relationship and Marian accuses him of adultery.

Investigating the brutal murder of a homeless man bludgeoned to death with a brick, Joel and Fearless follow up on a tip from Teresa and discover two filmmakers who pay vagrants to become would-be gladiators and battle each other in the park; when the detectives realize that the filmmakers bribed a homeless drunk to land the fatal blows, they team up with Tom and David in the search for evidence to convict them.

Joel and Fearless search for killers who prey on unsuspecting families in their sleep and stake out the family that they believe to be the next target; when Andrea's reporting skills threaten their investigation, the detectives are forced to give her a front row seat to their trap.

During a search for a kidnapped newborn, Joel and Fearless uncover an obstetrician's plot to steal the babies of recovering addicts; on the eve of entering rehab, David gives Joel the heads-up that IAB is reopening the investigation into Emma's death; Tom takes the upper hand and neutralizes Trumper's attempt to coerce him into snitching on Joel; Kelly and Joel discover that although they each feel guilty for the death of their daughter, there was nothing they could have done to save Emma from the cerebral aneurysm that ended her life.

Joel and Fearless enlist Ray and Tom in an covert op to track down the thieves who killed Wisnicki and Chandler when the detectives assigned to the case fail to go after John Donadoni, the man behind the murders; when tailing Donadoni leads to Sabrina Fithian, Joel and Fearless break into her apartment to wire it, and stumble into a surveillance led by Katherine Pierce, a Robbery/Homicide detective who's been after Sabrina, and knows that Sabrina and her partner Rachel are the cop killers they're after; after Donadoni threatens Kelly and Willy, Joel lets Donadoni know that Donadoni's mother can also find herself in danger; at Joel's urging, Katherine gets herself reassigned to their squad and gets Ron to assign them to her task force; Sabrina is captured after the team interrupts her latest burglary, but not before Sabrina wounds Katherine and then shoots a two-timing Rachel with Katherine's gun; Joel warns Donadoni that he's a marked man, no matter what happens to the case against S

Bank robbers attempting to flee the scene end up at a local shopping mall and take several hostages, including Teresa, whose ""shoot, don't shoot"" lessons at the academy come in handily at a critical moment.