One hundred thousand dollars carried in the express car of train No. 3 is the prize sought by Gregg and his band of outlaws. Two of the gang board the train at the yard, while the rest of the band hide along the track near Black Rock, where the holdup is to take place. Gregg and his lieutenant enter the telegraph station at Black Rock and bind Ruth, the operator, to her chair, to prevent her from telegraphing word of the holdup. Later, due to Gregg's carelessness, the telegraph station catches fire. The holdup is successfully perpetrated. Tom, Ruth's sweetheart, is the express messenger. Realizing what has occurred the boy bolts the door of the express car. A moment later, a bullet stuns him. The outlaws compel the train crew and passengers to descend. A leaky throttle in the locomotive causes the train to start. Before the desperadoes can leap aboard, the train has run wild. By extraordinary ingenuity, Ruth manages to send a message over the wires with her teeth. Sheriff Storm and his posse are immediately rushed to the scene, while a locomotive is dispatched to head the runaway off. The Sheriff rescues Ruth from the blaze in the nick of time. The baffled outlaws flee with the posse close behind. The desperadoes take refuge in a cabin and a battle ensues. Gregg makes his escape when the posse closes in on the gang. Storm follows the man. Coming to a cliff, Gregg forces his horse to leap off. landing in the river fifty feet below. Undaunted, Storm follows and captures the outlaw. The runaway train is overhauled and brought to a stop. Tom revives and, opening the door of the express car, reports what has occurred. A month later, the directors of the road show their appreciation of the lovers' heroism by presenting Ruth and Tom with a substantial check.