Fourteen days ago, CIA headquarters in Langley, Virginia, received a cryptic message from an agent operating deep undercover in Russia.'He has betrayed us and wants to go to war.' Unable to make contact electronically, the Director of Operations turns to its most deadly field officer - special agent Will Cochrane. His mission is simple: infiltrate the secret submarine base in eastern Russia's Avacha Bay, locate the agent operating under the codename 'Svelte,' and decode his message - or die trying. But after successfully penetrating the base, Will finds Svelte bleeding and near death, his last words a final clue. Now, Will must find out what they mean...and discover the identity of a mysterious figure known only as Sentinel.