Danny contemplates retirement, but Erin steps in and requests his help for a case involving her ex-husband. Frank clashes with the new mayor, while Eddie and Jamie pose as a couple.
Frank causes family tension when he assigns Jamie to guard Danny after a hit is put on him; Frank tries to stop his grandson from seeking revenge after he's attacked; Eddie gets a hostile new partner.
After a terrorist attack takes place in the Middle East, Frank is on high alert as a threat to New York City may be next.
Danny receives a chilling message from a possible serial killer. Erin considers applying for a judgeship, and mayoral candidate Katherine Tucker believes Frank is secretly investigating her husband.
Jamie and Frank oppose each other's viewpoints over the public's treatment of cops, after rowdy teens pour water on two rookies; Danny and Baez investigate a man who preys on the elderly; Erin is forced to admit her wrongdoings.