The Vegas own an oil rich ranch and Calhoun is after the mineral rights. He gets Carlos Vega to run huge gambling debts. When Carlos' sister who is half owner arrives, Calhoun tries to have her killed. Roy finds a clue and this leads him to Calhoun's offshore gambling ship.
The Rough Riders are called in to help save Master's stage line. Taggart has his gang robbing the stages and shooting the drivers. When Buck drives the next stage, Taggart's men rob it and then make it look like Roberts is part of the gang.