Plunge (Plunge #2)

After discovering a corpse upon the Sinnikik Atoll, Moriah Lamb leads a team to hunt for other castaways, while Gage Carpenter begins the exploration of the ghost ship Derleth. But there’s something down there in the icy darkness of the Arctic sea, something that doesn’t want to be found. And it isn’t any safer on land.

There are things waiting for the search party in the mountain caves, things that were once human ... and aren’t quite anymore.