Forensic investigator Darby McCormick queues to enter Boston Police Headquarters on a freezing winter morning. Lured back to her hometown to help solve a cold case, Darby won't get far inside the station - and this will be no ordinary homecoming...Because someone suddenly takes a woman hostage and a stand-off ensues. The man has explosives strapped to himself and other bombs hidden around the city, rigged to explode - every three hours - until he gets what he wants.Working desperately against the clock, Darby realizes she is trapped between a kidnapper who would kill to expose the truth and people who would let others die to hide their lies...