An engineer's new experimental stream-lined train rushes to deliver iron lungs to victims of infantile paralysis.
Railroad president B. J. Dexter (William Farnum) learns from his daughter Ruth Dexter (Sally Blane) that an iron lung saved a life. Engineer Tom Caldwell (Charles Starrett) tells the board of a faster train he invented, but Dexter rejects it. Ruth asks Tyler (Theodore von Eltz) to send for Caldwell, and Tyler decides to build the train. Tom tells Ruth about it. B. J. Dexter asks to go on the trial run with Tyler. The train is not fast, and Caldwell wonders what is wrong. B. J. Dexter tells Tyler to drop the project. Tom criticizes B. J. Dexter and argues with Ruth. Allen Dexter (Hardie Albright) tells his father he is leaving to work at Boulder Dam, because his new ideas are not accepted. B. D. Dexter recalls railroad history. The train is exhibited at the Chicago fair, and Crawford (Arthur Lake) gives Tom an idea.
Ruth cries and tells her father she is going to California. Caldwell shows Tyler the improvement and learns that Ruth left. At Boulder Dam a doctor finds infantile paralysis and fears it may spread. On a train Ruth meets a woman crying because her son got infantile paralysis at Boulder Dam. Ruth goes there and looks for Allen before the quarantine. Allen becomes ill and collapses. Ruth learns that Allen needs an iron lung by noon tomorrow. B. D. Dexter learns the iron lung is too big for a plane. Caldwell tells him to use his faster train. Dexter is reluctant, but Tyler persuades him to use the Streak. Bronte (Irving Pichel) is accused of helping an unfriendly country but knocks out the man arresting him and gets on the train.
The Silver Streak travels fast and has several narrow escapes as it crosses the Mississippi; but it must go faster and begins to average more than a hundred miles per hour. Caldwell puts O'Brien (Edgar Kennedy) in control while he gets coffee. After two more narrow misses, O'Brien says it is insane. Bronte knocks out O'Brien and tells Caldwell he is stopping the train. They fight as the train gains speed downhill to 140 miles per hour. Caldwell knocks out Bronte and takes control. The Silver Streak arrives on time, and Ruth thanks Tom Caldwell.
This story dramatizes the value of new inventions in railroading by its extra speed saving a life with an iron lung breathing machine, suggesting that new technologies can improve living conditions if men in powerful positions will allow them to be used.