From publisher blurb:
In Tomb in the Depths, a group of level-5 adventurers learns of a fabled location. A ship cemetery that somehow attracts more and more vessels and crafts to it. Pirates and sailors avoid it at all costs, but rumor has it that a thousand-year-old vault rests at the bottom of the sea, right under the crashed and stranded ships. Fishermen and locals have vague rumors and twisted stories about the origins of this place. There is a gnome named Farris Zamilikus who seems to know more of the truth...
The adventurers are up for a great surprise when they realize their task might be more dangerous than expected. Besides the local fauna and the environmental complications, the vault is not abandoned, and while it is loaded with treasure, it is also a king's tomb. The individual that rests there won't let some pesky grave-robbers steal what's rightfully theirs.