A year after Atalanta and Damien were brought together by the Pythia, they are once more called together. All around the Mediterranean there are strange storms, mysterious disappearances, and gruesome murders. Though the events are seemingly unrelated, Calista is convinced they are the work of Poseidon. She tasks Atalanta and Damien to put an end to the destruction. With old allies and new, they must face sea monsters, pirates, fearful mortals, and sirens on their way to finding, and stopping, Poseidon.