A strange case takes Dr. Jessica Coran and her team on a 70-foot dive off the Coast of Nantucket Island to do a crime scene investigation inside a sunken yacht, the Promises Fulfilled. Within the eerie confines of the underwater sepulcher, Jessica and the others discover more questions than answers. Sadly, beyond the all-important Senator's corpse, the team must deal with, there's his wife and two young children.

Even with the help of the famous undersea explorer, Dr. Bob Ballard of Titanic fame, on raising the yacht, more questions mount as there is no evidence whatsoever as to precisely how the ship went down, and later, on autopsy, Jessica discovers no one on board had saltwater in their lungs. They did not die of drowning, but were dead before the ship went under. Furthermore, they died of imploded veins, vessels, and arteries, and there is not a scratch on the hull of the ship.

This mystery is one for the books, and it cannot be solved without the help of every member of the team, all pitching in, including her faithful colleague John Thorpe (JT) as well as a dogged investigative reporter named Hunt, and a "deep throat" nameless informant.

The series began with Killer Instinct and Fatal Instinct, and is now up to 15 titles.