Having just led his men to victory over the Persians, Greek sea commander Carpus knows the victory does not belong just to him, but also to the aquamarine he wears around his neck. The stone, originally a gift from Poseidon the sea god to Carpus' grandfather, is the most valuable item Carpus owns. But the sea god has always regretted giving away the stone, and when a storm rises from the ocean depths, Carpus knows who's behind it. Poseidon, come to steal back what he freely gave decades before.

But Carpus is wrong. It's not Poseidon who carries him from the sea and gives him more intense pleasure than he's ever felt. It's Hesiod, Poseidon's son, a merman sworn to seduce the stone away from Carpus. Or die trying.