On a beautiful May morning at New York’s John F. Kennedy airport, two planes have just departed for San Francisco—one a 757, another a smaller Airbus A321. At a security checkpoint, TSA agent Bernice Adams finds a postcard of the Golden Gate Bridge bearing an ambiguous—perhaps ominous—message. Her supervisor dismisses her concerns, but Bernice calls security and soon Ben Waterman arrives. A senior Homeland Security agent, still grappling with guilt after a disastrous operation in which hostages were killed, Ben too becomes suspicious. Who left the postcard behind, which flight is that person on, and what exactly does the message mean?As Ben scans the passenger manifests, his focus turns to t