The Devil and the Dark Water
by Stuart Turton
2020, Sourcebooks Landmark
The Devil and the Dark Water is Stuart Turton's second novel, the first being The 7 1/2 Deaths of Evelyn Hardcastle. The two are not connected, but I think 7 1/2 Deaths is the better book, and so would suggest reading that first, unless you especially like 17th century sailing mysteries.
The Devil follows the great detective, Samuel Pipps, on his most confounding case yet -- or rather, it follows his bodyguard and Boswell, Arent Hayes, as Samuel is imprisoned, and must investigate by proxy. The two are boarding a ship undertaking the long journey from Batavia to Amsterdam -- Pipps in chains -- when a mysterious leper appears, warns them of doom, and then bursts into flames.
So starts a twisty mystery on a cursed voyage; the ghost of the leper haunts the cargo hold, a demonic symbol appears in impossible places, and an unidentified ship dogs their convoy at night, only to disappear in the dawn. It emerges that many among the passengers and crew have a history with the devil known as Old Tom, or alternatively, a brutal mass-murder conducted by agents of the United East India Company years ago; these may be connected. Arent collects clues and fights to resist the rising panic taking hold of the ship, but with Pipps locked away in his cell and Old Tom becoming more bold, things look more and more hopeless.
This is a very detailed and twisty mystery, and despite the supernatural element, manages to remain a mystery and not a fantasy. It also sort of a historical novel, being set in 1634, although Turton is very clear in stating that the book is not intended to be especially historically accurate in any aspect; it still does well enough that there aren't any too glaring historical inaccuracies. However, it is primarily a character-driven re-imagining of Sherlock Holmes, with Sherlock safely removed to the fringes of the story to allow the supporting characters to run rampant. It is well worth reading, especially if you are in the mood for a somewhat dark and twisty supernatural mystery.