Danny and Lena's investigation into a robbery gone wrong quickly turns personal; Sean and Jonah face rising tensions with Boston's firefighters; Sarah clashes with boyfriend Seth over family discipline.

Following the release of Ben's killer from prison, Jonah continues to struggle with anger and grief confronting the killer and putting family bonds to the test, and Mae and Sarah face painful truths that could change everything. Meanwhile, Danny and Lena take on a high-stakes case that uncovers deep-rooted secrets and forces unlikely alliances.