Leviathan

Monsters are real.
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.
The final chilling book in the blockbuster Fathomless series delivers a terrifying roller-coaster ride of epic proportions.