In the Micronesian Islands, a top-secret, US government-sponsored undersea lab conducting vital biomedical research on a rare jellyfish known as the Blue Medusa suddenly disappears. At the same time, off Bermuda, a bathysphere is attacked by an underwater vehicle. Stranded half a mile below the surface, its passengers-including Zavala- are left to die. Only Kurt Austin's heroic measures can now save them from a watery grave.

Austin, suspecting a connection between the two mysterious events, puts the NUMA team on the case. He has no idea what he has just got them all into - a hideous series of medical experiments . . . an extraordinarily ambitious Chinese criminal organization . . . a secret new virus that threatens to set off a worldwide pandemic. Austin and Zavala have been in tight spots before, but this time it's not just their own skins they're trying to save-it's the lives of millions.