After the Kid wins another duel (over a man who claimed the Kid was cheating), the boys are contacted and offered a job by a man called ""Doc"" Donovan. They are to come with him into Mexico, to rescue a hostage from Mexicans who only want their rightful money.

The Kid senses that Doc knows who they are, but they cannot be certain, and why would he hire them instead of collecting the fee?

They manage to sneak out the hostage, Mr Zulick, but are chased by the kidnappers. After a daring stunt, they lose their followers, and Mr Zulick can continue on his journey. Then, Doc turns them over to the sheriff...

But where is Mr Zulick headed and why? And why does the sheriff want to let Heyes and the Kid go?