A Splendid Hazard by Harold MacGrath ( Classics Series)

A foremost authority on pirates, a megalomaniac descendent of Napoleon, a secret agent, an opera singer, an unspoiled rich American beauty and others gather at a mansion for what was thought to be a pleasure cruise, but is a search for buried treasure. This adventure is told mainly through the eyes of an adventurous journalist, but the deepest motives of many of these people are traversed as events rush towards the conclusion. Who will panic, who will hide, who will step forward, who will protect whom. The mystery of the treasure ends up being secondary to how each person reacts to the pressure and temptations of which they are thrust. So the real climax, as in most MacGrath stories is in how true character and indeed heroism show in people, both high-born and "common". This is an enjoyable and gripping character study/revelation