A dead artist. A cursed lighthouse. A town built on secrets that should never have surfaced.

When bookseller Maren Halloway is handed a strange sketch covered in impossible geometric patterns, she thinks it is little more than a troubled friend's latest obsession. By the next morning, that friend is dead on the rocks below Devil's Cove.

What begins as one suspicious death soon drags Maren into a nightmare buried beneath the salt and fog of Port Haven. Another artist vanished decades earlier after uncovering the same patterns. Old family names keep appearing where they should not. Threats arrive in blue paint. And hidden beneath the lighthouse lies evidence that the town's most powerful families have been guarding something for generations.

As Halloween approaches and the tides begin to shift, Maren realises Port Haven was never just a picturesque seaside town. It was built as a prison. And whatever has been sleeping below it is starting to wake.

To uncover the truth, Maren must follow a trail of vanished women, coded journals, secret tunnels, and lies old enough to poison an entire town. But the closer she gets to the heart of the mystery, the clearer the danger becomes: some secrets are protected with murder, and some truths are powerful enough to unravel reality itself.

The Mathematics of Tide: Secrets Beneath the Surface is an atmospheric coastal gothic mystery packed with small-town conspiracy, female-led suspense, occult undertones, and a slow-building supernatural threat that lingers long after the final page. Perfect for readers who love eerie seaside settings, buried family secrets, and mysteries where the truth is far stranger than anyone imagined.