During the American Civil War the Confederates organize raids to steal shipments of horses from the Unionists which are desperately needed for the Union war effort. Union army officer Lex Kearney volunteers to undertake a covert investigation to find out why the North's supply of horses has suddenly diminished. Because of the top-secret nature of his mission, Kearney is forced to distance himself from everyone he knows, including his wife Erin and son Jamie. In order to make his camouflage more plausible he is dishonorably discharged from the army for cowardice in battle. Falling in with the gang of jayhawkers and Confederate soldiers who have been conducting the raids from a remote calvalry post, he gradually gains their trust and is put in a position where he can discover who has been giving them secret information revealing the routes of the horse shipments.