When a computer scientist flees to Britain with highly classified information, the United States turns to the UK for help. Task Force Sabre, a division of British Intelligence tasked with the dismantling of terrorist organizations around the globe, is pulled from a high-value mission to apprehend the renegade computer scientist. Alex Michaels, along with his partner and brother, former Special Boat Service soldier Scott Michaels, tracks the scientist down and prepares to hand him over to federal authorities. That is until they are ambushed by an unknown enemy and their prisoner is kidnapped. Along with NSA cyber analyst Kelly Taylor, Alex and Scott pursue the scientist across the United States and, in doing so, uncover a conspiracy protecting an intelligence secret so devastating it could spark a global war. Fighting forces on both sides, Alex and Scott will have to muster all their skills to find out the truth that some would kill to discover and others to protect: what is Tier Zero?