From the back cover:
A tale must be told of Autumn's death...
Like a fresh spring bud vulnerable to a sudden frost, your Covenant was once perilously frail. However, during many hard years you and the other Magi labored to garner a small measure of magical might. Now, after the hardships of a long gruelling toil, you can rest upon the laurels of achievements past. You are at Autumn, the bloom of your power.
But lo, Winter now looms on the horizon. A great evil is mounting and it takes its strength from the burning pits of Hell. This evil has been doing its black work from within your covenant for decades, without your slightest knowledge. Be forewarned: if you cannot best the evil you have bred, you endanger your mortal soul.
A Winter's Tale
This Ars Magica supplement is part III in the Four Seasons Tetrology, and follows in the footsteps of The Tempest. Herein the Storyguide will feed the information needed to organize the descent of your Covenant from Autumn to Winter. This book consists of several interrelated adventures that detail the collapse and perhaps destruction of a once proud Covenant.
The characters must come to grips with the malign threat posed by a band of Diabolists who aspire to bring about Armageddon. Unbeknownst to the characters, they have been at the root of the Diabolists' machinations from their very beginnings. Now the Magi must undo what has gone in the past or their Covenant will not merely pass into Winter, but may pass from existence.