Hard Aground — James W. Hall

450 years ago a treasure ship went down. In Miami, the heat hasn't let up yet... Hap Tyler sailboards on Biscayne Bay, hears voices, seduces young women, and lives on the edge of history in his family's old-money mansion amid Miami's pastel glitz. But while Hap stumbles around in the shadow of his more successful older brother, Daniel, a tangled web of deception and greed is being spun around him - a web that leads Daniel to his death.
Trying to solve his brother's murder, Hap collides with a 450-year-old secret: the disappearance of $400 million in sunken Spanish plunder. Daniel's upscale girlfriend is close to digging up the treasure, an avaricious senator has already tasted it, and a stone-cold killer will stop at nothing to bring it home. For Hap, a dark and bloody vein of Florida - and family - history has been opened. And the only way to close it is through a modern ritual of violence and truth.