When a subway station shootout leaves a detective critically injured, Danny and Lena race to determine what really happened before mounting public pressure and political fallout derail the investigation.

Danny and Lena follow a lead in the attack on Detective Rodgers with her father's help, finding themselves in an intense standoff with a dangerous biker gang.

When a series of murders begins mirroring the infamous Boston Strangler killings, Danny and Lena race to stop a copycat killer before he strikes again. As panic grips the city, Jonah and Sean jump in to help track down and arrest the killer. Also, Danny faces a career-defining promotion while Lena uncovers a lead that could link the attack on Detective Rodgers to a powerful figure.