Something is wrong in the countryside. The corn crops are turning. Old men wander off in the night with milky-white eyes. A courier drops a shipment of food and strange chemicals at the edge of the hills, and nobody sees him leave.

A Ritual Most Foul is a 144-page Old-School Essentials supplement built around a single question: what happens when a cult gets what it wants?

The book opens with three new character classes. The Holy Knight is a devotee of Law — sword in one hand, divine authority in the other, and a dueling ability that turns a successful hit into a setup for maximum damage on the next. The Inquisitor brings a custom spell list built for investigation and coercion: Augury, Void Stare, Whisper, Speak with Dead, Incite Frenzy. The Zealot rounds out the trio for referees who want players operating in morally contested territory.

The Cult Domains section is the book’s engine. Seven cult doctrines — Plague, Revelry, Symmetry, Moon, Nightmares, and more — each get full stat blocks for rank-and-file members and cult leaders, a plot generator, a rumors table, a keyed encounter list, and a signature magic item. They’re modular enough to drop into any campaign and specific enough to feel like real threats.

Three adventures put it all into play. In Cultists’ Wake follows the trail of a Plague cult into a flooded crypt, where Lord Straton’s disturbed tomb and a cultist’s annotated map point somewhere worse. As Above, So Below sends the characters into a domed hilltop ruin caught between three factions: the cult, a chitin devil running its own game, and something green that slipped up from underground. The Tower of Six is a ticking-clock dungeon — the ritual starts on Day 1, and if the party doesn’t stop cult leader Luchus before sunset on Day 3, the She-Maggot tears through the veil.

Writing by Zac Goins. Maps by Lydia Pfister.

A Ritual Most Foul is a 144-page A5 hardcover compatible with Old-School Essentials.