Danny believes a serial killer is on the loose when two separate murder victims are identified as members of a group charged with the gang rape of Lily Rivera. Danny and Jackie chase down another man in the group and he directs them to Lily's brother, who swore to kill each of them when they avoided conviction due to inconclusive DNA evidence. After his alibi checks out, they follow a ballistics hit linking the gun to a gang banger. The gang banger explains that the gun was taken from him by Detective Freehill, the same detective who investigated the Watkins rape. Danny and Jackie track down Freehill as he is holding a gun to the last member of the group and Danny manages to talk him down. Meanwhile, Erin faces off with her ex-husband Jack Boyle in court and warns him against getting Nicky's hopes up about moving back into town. Frank helps a jaded young man, who has a won a contest to be "Commissioner for the Day", cope with the murder of his mother by committing to find her killer.