From the publisher website:
Power from Beyond the Earthly Sphere
The power of Hermetic magic does not extend to the Lunar sphere, so what happens when a powerful demon incarnates himself in a body which is apparently from that realm? Can the magi defeat such a powerful enemy on their own, or must they rely instead on a miracle from God?
The Fallen Angel is a story for use with Ars Magica Fourth Edition, but which can be easily adapted for use with any other edition of Ars Magica. The Fallen Angel takes place in 1220 in Ireland and the Isle of Man, but information is included which allows this scenario to be adapted to alternate locations and times within Mythic Europe.