The tide-turning fantasy of ships, saints, and equations, Saltwater Arithmetic follows a girl who can read the sea the way others read ink. Eida Quay was born beneath the glass-lit piers of Glassharbor, where the water keeps accounts and every debt is written in salt. She grew up believing numbers could be kind—until Kade the Tide-Keeper, a rogue auditor of currents with a smile like a cracked compass, used her gift to unlock the Ledger Reef and left her family's name to drown in its balances.
Vowing never to be tallied again, Eida flees to the counting cloisters of Xochi Reef, where she learns the forbidden proofs of wavecraft—how to knot a current with a phrase, how to divide a storm with a line of chalk, how to turn grief into buoyancy. With a Tidal Abacus made from shark bone and a Knucklebone Sextant that throbbed once inside a leviathan, she plans to restore what Kade stole: her mother's chart, her brother's future, and the unbroken sum of her own heart. But a new calculation has surfaced in the archipelago of Las Nácaras: the Drowning Sum, a murderous curse that balances the living against the lost, taking one breath for every oath kept, one life for every map completed.
When Glassharbor's salt clock cracks and the Empyreal Ledger begins to sing, Eida is forced into a truce with Kade. To break the Drowning Sum, they must unspool arithmetic written in whale-song, navigate the bone-lantern markets of Port Hecate, bargain with the Riverglass Pages of Calderon Spire, and face an Auditor who drinks memories like rain. Old friends turn into rivals—the navigator Rui with her rust-bright skiff, Mother Galaxa of the Counting Temple—and new allies prove unsteady, like Tamsin Rye, a thief who steals only from the future. The sea keeps perfect accounts, and its magic plays with heads and hearts: every proof demands a price, every theorem wants a witness. Eida has always trusted the math inside the waves, but when the numbers start to look like her own name, she isn't sure she can.
Continue the voyage in Brine Logic and The Theorem of Tides!
Also by Kwame Vasquez:
The Delta City Cycle:
- Loamlight
- Rust Cathedral
- Floodplain Choir
Silt & Starlight
