Spontaneous Combustion by Thom Nichols
Approx. 137,050 words.
Published on October 23, 2010.
A werewolf doesn't transform into existence, it is exchanged into this world from a parallel universe ruled by evil magic. Greg spontaneously combusting finds himself in that world. Befriending strange people, Greg finds that he was brought here for a reason. Hunted by the werewolves, he has to learn to use evil magic to try to escape and return to his world. But, it exacts a terrible price.