Hell's advance is not proclaimed by clouds of brimstone and floods of blood. Evil creeps close with soft smiles, in respectable raiment and whispering honeyed lies. The darkness offers what you desire. The first murders are subtle, the initial corruptions hidden in the shadows. The brimstone and blood will come later. But they will come. Step by step evil advances, until at last nobility is sundered, the holy altars lie abandoned, and the virtuous cower in silence. Then the land will drown in blood. Unless you can stand against the evil.
I haven't published a focused campaign setting / campaign for Ars Magica since I wrote Mistridge for 3rd edition. But here we have a brand new Saga set at the edge of the Normandy Tribunal...
I've written The House of the Crescent Sun to be system agnostic, but the PCs are founding a new settlement (i.e. independent Covenant, or a Vassal Covenant) in order to claim and investigate two magical sites in a remote valley... so this is a classic new Saga start - although it also works as a spin-off from an existing Saga.
The players do a deal with the local count, start building (or rebuilding), but then uncover an insidious infernal conspiracy. And as the darkness engulfs the nearby city they must battle against the rising power of hell.
The House of the Crescent Sun balances set-piece adventures with a sandbox setting full of strategy an impactful choices. Each story gives the PCs chances to gain friends and enemies amongst their neighbours, and guidelines are included on down-time diplomacy between adventures - a custos could have plenty to do while the magi are studying each season! So when the forces of the infernal make their move then the characters' actions will determine how strong the darkness is, and who will stand with or against them.
Backers get: the main Campaign book; a Players' Guide booklet; system notes on running for Ars Magica (or 5e or Mythras), with stat blocks, new infernal powers, etc.; and digital handouts. The campaign book and players' book feature full-colour pages with all hand-drawn art, in a medieval illuminated manuscript style.
Skirmishes, assassinations, court politics, military strategy, thefts, diplomacy, sieges, and demonic conspiracies, in a campaign where choices matter and where demons are more insidious than any that the players have faced before.