The interests which own the smelter offer to purchase Williams' mine, provided it assays a higher grade of ore than that produced by Walker's mine. The rival mine owners thereupon load a couple of cars with ore and consign them to the assayer. Knowing that Walker's mine produces a richer ore, Williams endeavors to hold up his rival's shipment. Several of his men attack the engineer of the freight and lay him low. Helen, the operator at Lone Point, sees the attack. While the train crew gives battle to the desperadoes, she dons overalls, climbs into the engine cab and pulls the throttle wide open. Williams, waiting at the assayer's office, receives a 'phone message from his foreman telling him how Helen has frustrated the plot. Undismayed, the scoundrel succeeds in changing the billing cards on the cars containing his ore and Walker's ore. Walker, confident of success, is dumbfounded when the assayer informs him that the cars bearing Williams' cards contain the better grade of ore. Helen suspects something wrong and makes an investigation. As the result, Williams' contemptible trick is revealed. Frustrated, the scoundrel endeavors to escape, but Helen again interferes and Williams is placed under arrest.