A Union Cavalry outfit is sent behind confederate lines in strength to destroy a rail supply center. Along with them is sent a doctor who causes instant antipathy between him and the commander. The secret plan for the mission is overheard by a southern belle who must be taken along to assure her silence.

Little David Gordon lives in the jungle with his parents Ruth and Fred, along with their servant Nona. David likes living there while his father captures wild animals; he's made friends with Bomba the jungle boy, who has shown him a great deal about life in the jungle. One day two adventurers come looking for ancient treasure in the shadow of a live volcano.