A band of cruel fighting men known as the Shadow Riders is running wild across Arizona. Their name, striking fear in residents and lawmen alike, reflects their method of warfare--appearing from nowhere, vanishing again into the mountains where their fortified hideout stands.

The Arizona Rangers are given the job of rooting out the bandits, many of whom are known to have been recruited from the ranks of Army deserters. There is only one way of breaking up the gang: from within. When Tyrone Cannfield returns to the Rangers, he accepts the dangerous assignment. To achieve his goal he needs to pose as one of the outlaws. Alone in the mountain citadel, he must find a way to stop the Shadow Riders with or without the help of Bobbi, the enigmatic young woman he encounters there.