Danny investigates a case in which Stephanie, an expectant mother, was assaulted by a trio of thugs playing the "Knockout Game" while walking with her husband. The trauma she endures causes her to lose her baby, which had taken a very long time for the couple to conceive, and both are absolutely devastated by the completely random, senseless attack. Stephanie is able to give Danny a viable lead: the name of a drug dealer who frequents the area when she was attacked, which she heard moments before being attacked. The drug dealer turns up dead, killed by a gunshot to the stomach, and evidence at the scene makes Danny realize that the man responsible for the drug dealer's demise was Stephanie's husband, Mike. Danny is torn between doing his duty as a cop and arresting Mike, or disposing of the single piece of evidence tying him to the crime, empathizing with Mike's need for vengeance. He ultimately arrests Mike, but the Grand Jury opts not to indict him based on confession and testimony indicating that the murder was an accident. Meanwhile, Frank wrestles with promoting a deserving candidate within the department, fearing that the officer's personal ties to Frank and his family might be viewed as favoritism. Erin also struggles with her own feelings about Jack Boyle after he begins to push for more of a romantic relationship again.