The Devil and the Dark Water by Stuart Turton

It’s 1634 and Samuel Pipps, the world’s greatest detective, is being transported to Amsterdam to be executed for a crime he may, or may not, have committed. Travelling with him is his loyal bodyguard, Arent Hayes, who is determined to prove his friend innocent.

But no sooner are they out to sea than devilry begins to blight the voyage. A twice-dead leper stalks the decks. Strange symbols appear on the sails. Livestock is slaughtered.

And then three passengers are marked for death, including Samuel. Could a demon be responsible for their misfortunes?