Someone is killing soldiers in a Union Army regiment. But it's not the Confederate enemy. When a Union soldier is found dead on the outskirts of the camp, his neck sliced open from ear to ear, it's just another grim tally in the brutal war of attrition between the North and the South. But when another, and yet another soldier is found with his throat slit, an uneasy mood falls over the Union regiment. Who is killing these soldiers, and what does the strange mark on the dead men's foreheads mean? A young Union lieutenant and an eccentric field surgeon are ordered to get to the bottom of the killings. The two officers' strange task, and the killer's identity and motive, combine into a gruesome tale of murder amid warfare.