Alexander's Treasure (Sam Reilly #22) by Christopher Cartwright
This is a stand-alone book. You don't need to read any of the prior 21 books to enjoy it.
Sam Reilly is invited to give a lecture about marine archaeology at "The World" a 644 ft 2 inches luxury yacht that is home to the wealthiest people in the world - staterooms are sold for millions. At the end of his lecture, he's approached by three very rich people: Arlie Chapman - 45 y/o CEO of a very large oil company, Shireen Doyle (Queenie) - a 50 something widow and renowned collector of fine arts and antiquities from Sydney, and Ashton Grey - a seventy-odd-year-old retired broker from London known for his uncanny luck in market predictions. All of which have a proposition for Sam.
As it turns out Shireen Doyle was looking for oil in the Black Sea and found a gold tetradrachm depicting the facade of Alexander the Great with the obverse depicting an image of Zeus. These coins were traditionally minted in silver, but it is rumored that Alexander, fearing an assassination plot, had lots of them minted in gold - thus Alexander's Treasure - and it was hidden. Up to this point, it is only a legend, but upon authenticating the coin, there's a possibility that the treasure exists.
Shireen hires Sam to look for the treasure, but as he leaves the conference, he's drugged and taken captive after falling off The World - presumed dead.
Tom Bower and his wife/partner, Genevive, start looking for Sam and soon deduce that he's been kidnapped and start their own search for Alexander's Treasure, knowing that it's the only way they can save Sam.
So we have several competing people looking for the treasure and we don't know who's behind Sam's abduction nor who's innocent or guilty. Now Sam and Tom are on the hunt to find the treasure, and there is much more at stake than mere wealth.
Narrated from the third person point of view, this is an easy, fast read. The plot twists and turns keep you involved to the very end. The characters are three-dimensional and fascinating. I had trouble putting it down.
Highly recommended!