Wizard Squared

When the staff of Witches Incorporated receive a visitor from an alternate reality, they are shocked to learn that life in the parallel world next door is anything but a bed of roses. And it's all because of Gerald Dunwoody. At a crucial moment in time, their Gerald turned left - but the alternate reality Gerald turned right. Now the parallel world next door is in the grip of terror, staring down the barrel of a thaumaturgical war.
A war that threatens to spill across the dimensions and plunge every reality into nightmare. The only person who can stop a rogue wizard gone mad is another rogue wizard. But what do you do when another rogue wizard is nowhere to be found?