Disguised as a gambler, U.S. Marshal Tim Donovan Tim McCoy) rides the Black Mountain Stage which is held up by Pete Smith (Ted Adams) and his gang. Tim and his pal, Tombstone (Ralph Peters) pursue --- no, not on foot as their horses were tied to the stage --- and find the robbers trying to open the strongbox. The outlaws flee and Sheriff Clay Matthews (Rex Lease) arrives and arrests Tim and Tombstone as the robbers. Judge Harper (Frank LaRue), also a passenger, frees Tim and Tombstone. Tim finds a charred money-bag in the Judge's fire place as the bandit's, unknown to the Judge, had used his house as a rendezvous. Tim and insurance investigator George Harris (Edward Peil Jr.) join forces and discover that stage agent Biff Hunter (Jack Rutherford) and town banker Emmett 'Alden 'Stephen' Chase') are confederates of the gang. The sheriff still suspects Tim and gives him 24 hours to get out of town. Tim captures Bart (George Chesebro), one of the gang wounded in the gun battle following the robbery, but Bart is shot from ambush just as he is about to give Tim the names of the gang leaders. The sheriff captures Pete, Biff and gang lieutenant Jim Miller (Dirk Thane) but Tim and Tombstone, fearing the capture will spoil their plan to find the leaders and the gold, set them free. The sheriff offers a $500 reward for the capture of Tim and Tombstone.