Bill Browning heads the trauma unit at San Francisco's busiest emergency room. With his ex-wife and daughters in London, he immerses himself in his work and lives for the little time he can spend with his children. A rising star at her teaching hospital, Stephanie Lawrence has two young sons, a frustrated stay-at-home husband, and not enough time for any of them. Harvard-educated Wendy Jones is a dedicated trauma doctor, trapped in a dead-end relationship with a married cardiac surgeon. And Tom Wylie's popularity with women rivals the superb medical skills he employs at his medical centre, but he refuses to let anyone get too close.

These exceptional doctors are chosen for a unique project: to work with their counterparts in Paris in a mass-casualty training programme. When an unspeakable act of mass violence galvanizes them into action, their temporary life in Paris becomes a stark turning point: a time to make harder choices than ever before - with consequences that will last a lifetime.