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 reaction of events that will alter everything they know.