On the Mississippi, on board the Dispatch, Tex and Carson fill some members of the band of river pirates with lead. Then, thanks to the ex-pilot Mac Merrick’s information, they avoid a trap orchestrated by Captain Travis in cahoots with his lover, the beautiful Nadine. The girl, with her back put against the wall, reveals that the marauders hide on Spirit Island, inside a run aground boat. The rangers, supported by the sheriff of New Orleans, Nat MacKennet, blow up the pirates’ den and capture the gang leader, Mathieu, so that he will give the lie to the instigator, the vile shipowner, Coleman, in front of everyone!