John Wells is a CIA agent who has been in deep cover for years with Al Qaeda in Afghanistan - living, training and fighting, and even converting to Islam. When he gives no warning of 9/11, the CIA wrongly assumes he has turned traitor. Then, years later, Al Qaeda sends him back to the States as part of a sleeper cell where he is to await further instruction. That Wells is alive is the only good news his former CIA handler, Jennifer Exley, has heard in a long time. Her personal life is crumbling, the CIA stumbling beneath the weight of waging a worldwide and endless intelligence war. Then it all comes apart: the nation is brought to its knees when two bombs rock Los Angeles simultaneously, Exley receives a call from Wells. Though she's thrilled to hear from him, she can't help but think the timing's no coincidence. When Wells comes in to tell the CIA what he knows, he is treated as little better than an enemy. Though he's given the nation his life, Wells realises that he's lost its trust. He runs, leaving Exley as his only lifeline. In Iraq, American troops capture a Pakistani physicist, who the CIA hope will be the key to a number of mysteries, and Exley keeps Wells informed.But it's only when Wells receives the call from his Al Qaeda superiors that the pieces finally slip into place: a massive attack is in motion, thousands of lives hang in the balance - and Wells himself is to be the agent of destruction.