The Kindle edition of Cool Blue Tomb by Paul Kemprecos is offered free today by Amazon.
From the Amazon site:
A 50-million-dollar salvage operation. An expert diver dead at the bottom of the sea. An elegant mermaid in a black Porsche -- and an open invitation to dip into the troubled waters of her marriage. Cape Cod's Aristotle "Soc" Socarides, part-time fisherman, part-time private eye, is swimming with the sharks. Only problem is...he's the bait and blood is beginning to boil to the surface.
Soc didn't think he could get in much deeper, but he'd better think again. A family debt of honor comes due -- a debt only he can settle -- plunging him into the middle of a lethal search for buried treasure. Now Soc's about to discover how deadly the Cape's currents can be. Snarled in a net of smuggling, treachery, and revenge, he's finding out that no matter how down you go, nothing harder to salvage than the truth.
"Absolutely the best private-eye mystery I've read. I can't wait for the next one."
Best-selling Author, Clive Cussler
Me again: I'm a big fan of Kemprecos' Aristotle Socarides mysteries. Check this one out. you won't be sorry.