Darkling Rider (Short Story)

When invading armies to the East began conquering and slaughtering the people, the King's Riders, an elite fighting force who ride intelligent, Bonded horses, are magically bound to the Shadows to give them an edge. They get an edge, all right: they can travel through the Shadows at incredible speeds, attack without the risk of injury, and even communicate across vast distances. But when they lose their humanity to the Shadows and become a force for evil, there's only one way to stop them - the last Rider standing has to go in after them. Can he resist the pull of the Shadows long enough to destroy what remains of his brothers?