Erin and Anthony clash when Anthony's daughter is the sole eyewitness to a fatal shooting; Frank wants to punish an off-duty cop for his inaction during an armed robbery; Danny and Baez investigate a violent mugging.

Danny crosses paths with a criminal from a previous case when he investigates a gang attack with a shocking motive; Frank and Mayor Chase butt heads over an off-duty cop who goes too far making a political statement.

Frank and his grandson, Joe Hill, contend with a grievous insult to the memory of Joe's father; Erin and Henry work together to bust a scammer targeting the elderly; Eddie's captain takes suspicious interest in her efforts to locate a stolen puppy.

Jamie and his new intel team officer infiltrate a high-tech car smuggling ring; Frank faces off against the city's transit chief over a program that is causing officer injuries on the job; Eddie asks Danny to help her bust a cop impersonator.

Danny and Baez race against the clock to catch a serial killer targeting young women; Erin and Eddie clash when Eddie intervenes in a murder case and Erin's personal life; Frank must decide how to discipline his grandson.

Danny and Baez investigate a case of grand larceny tied to feuding crime families; Frank clashes with Mayor Chase when an influx of immigrants arrive in the city; Erin questions whether her district attorney campaign is compromising her day job.

Frank worries his longtime friend is hiding his true reason for returning to the city; Baez and her daughter are targeted by a criminal Baez once put away; Anthony is sucked into the inner workings of an underground crime ring.

Danny and Baez team up with Danny's old partner to find a copycat killer emulating a criminal's murders from a previous case; Frank and Mayor Chase battle over how best to handle the city's rising homeless population.