September, 1790. Greenwich.
William Godsalve is a northerner employed as a Clerk in The Sea Library - a four-hundred-year-old white marble institution devoted to collecting knowledge of the sea - and protecting people from its unruly power.
But with trade wars with the Dutch raging, the illegal smuggling of the precious, blue substance azumaris rife, and a strange, otherworldly seasickness spreading, the masses are beginning to question if the Crown is still in control.
Then a dangerous book written in the fifteenth century is stolen from the Library's most hidden collection and William is sent back to his hometown of Calderness to investigate.
In the rocky devilfishing town, William discovers Agnes, a school teacher hiding seasick children on a clifftop, who is desperate to find her missing patron before they run out of money and the children are given up to the authorities.
As the mystery deepens, dangerous connections between the sickness, the Library, the devilfish and William begin to emerge. Can anyone control the tide?
