e & Islands Detective Unit is called to a Martha's Vineyard ferry at midnight. She soon learns that the estranged son of Massachusetts' most famous political family is dead.

Was the victim, Daniel John Fitzgerald, murdered, or was he assassinated? Dan-Dan Fitzgerald was a preeminent eco-activist and whale advocate. His death triggers more deaths. Numerous suspects arise, among them the ferry crew, a megalomaniacal State governor, former Marines, a federal political lobbyist, and anti-whale shipping companies.

The investigation falters until Bourque realizes the key lies below the surface of Vineyard Sound, which leads to a tangled web centered on Cuttyhunk Island off Cape Cod.