After his latest mission goes disastrously wrong, veteran CIA black ops agent Emerson Kent is given one last chance to prove he still has what it takes to do his job. His new assignment: guarding Katherine, a code operator at a top-secret remote CIA 'Numbers Station' where encrypted messages are sent and received. When an elite team of heavily armed assailants lays siege to the station, Emerson and Katherine suddenly find themselves in a life-or-death struggle against an unknown enemy.