Cate Granger and Jack Monroe are enjoying life far away from the deep-sea horrors of their past ... but the ghosts still haunt them.

Russian billionaire and former friend, Sonya Borashev, tells them of a newly discovered cave in Antarctica that leads deep beneath the frozen continent. It's from these icy depths that Sonya believes a remnant species of megalodon shark has been set loose and that these ancient monsters are not only alive but thriving.

With a recent spate of horrifying attacks, Sonya leads an expedition to put an end to the monsters for good. And she wants Cate and Jack with her - whether they like it or not.

But beneath the dark ice, they uncover things even deadlier, even more dangerous than they could have ever imagined.