They'll fight the unseen evil, on the land or on the sea!

During one of the earliest blockade actions of the Civil War, US Marine Sergeant Alexander Philips witnesses an unspeakable horror. With no explanation, he finds himself in charge of a group of hotheads and misfits in a strange, unorthodox unit. His new commander is the enigmatic Lieutenant Addison Green, who knows nothing about the military, but a great deal about something else entirely. He comes bearing a collection of weapons geared towards fighting something other than confederates.

The marines of M Company take part in the Battle of Roanoke Island, doing a job far different than that of the other soldiers. They learn their true purpose-hunting the monsters that flood into the world in times of conflict. In the jungles of Roanoke, they find their first mission-to hunt the mysterious woman in white, a witch who commands the legions of hell and enchants the unsuspecting.

Their journey takes them through Saint Augustine and behind enemy lines to New Orleans, where they find an even greater threat to the Union than they ever expected.