Stony's brother George has been accused of murder and the Mesquiteers have returned to prove his innocence. But they find that Harvey rules the town along with his stooge Sheriff Gray and that George won't get a fair trial.

The arrival of the telegraph put Pony Express riders like John Blair and his pal Smoky out of work. A race will decide whether they or stageline owner Drake get the government mail contract.

When Professor Marsh disappears while searching for the lost city of Lukachukai, his daughter enlists the help of the Three Mesquiteers.