Overall, I enjoyed this immensely. I picked it up in a used book store simply on the strength of Chris Claremont's name--I still have no idea who the coauthor or the illustrator are--and he didn't disappoint.
The story is about Cassandra Dunreith, a comic book writer who spends her spare time as Lady Siobahn, a knight in a reenactment society. Cass is tired, worn down, and not as enamored of her alternate persona as she has been in the past, particularly given the churlish behavior of some of her fellow players, including the "King" she has sworn to fight for in this particular War. One night, she overhears a ritual which plunges her into a blurring of her reality and another world. Cass will be forced to confront the truth of her past, her family's deaths, and her own heritage before the War is done. The Shadow Riders have been summoned, and their price is simple: the War fought with real weapons, spilling human blood and claiming human lives--or Cass winning in single combat against their leader, the powerful and mysterious Mharyon.
My only regret is that this story is as short as it is, and that I've yet to find a sequel to it. Wonderful read, particularly for anyone who appreciates Chris Claremont.