It's been over six years since the events of Adaptive Instinct, and the survivors have settled into their lives aboard the Diana. They have their familiar routines on the modified cruise ship, where they feel relatively safe from the zombie threat that still plagues both the mainland and surrounding islands. That all changes when a cruise ship enters their waters, one that won't respond to their hails. With the lure of fuel too great to ignore, a team is sent over to investigate. What no one realizes is that there's already a threat aboard their own vessel; one that's going to set off a chain...

Since Fighting Instinct, the survivors have settled into their new homes back on land. While half of the group has chosen to remain living underground in the Black Box, growing crops on the land above, the other half has made the decision to settle in the container yard down river, gathering much of their supplies through scavenging. By trading equally between themselves, the two colonies have managed to create a sustainable, and even comfortable, existence. When a team of scavengers goes missing, however, and a platoon of hostiles arrives on the Black Box's doorstep, the camps are prepared...