A body caught in a boat wreck. A young constable acting unlike himself. A young woman determined that her Patrick has been replaced. An international conspiracy tied to Ireland. And a new task for Mr. Hardy: to find who killed the man on the sandbar, and how it connects to Constable Foster and his family.

When Mr. Hardy assists Constable Foster's mate "Ned" Kelly to pull a ship's boat off a sandbar, he is shocked to find a strangled body inside. But he is even more shocked when he learns that the last person seen with the dead man was Constable Foster.

Meanwhile, Aroha, the ferocious young Māori woman who has moved in with Foster has decided that the Patrick Foster who has returned from Napier is not the man she agreed to marry. Mr. Hardy and Aroha search for the real Patrick Foster, hoping to exonerate him, but a killer is on the loose, an Irish "Invincible." And Constable Foster may be more involved than they realize.