In a small, almost empty church, Rev. Hollingsworth [HB Warner] delivers a quiet sermon while his granddaughter, Jenny Hollingsworth [Natalie Wood], listens with rapt attention. As the Reverend’s voice falters, Jenny finishes a scripture quote he had started, and the two share a pew-side moment. Jenny, who calls him “Grandpappy,” reveals that she’s been raised in near isolation with him, and soon the Reverend passes away.
Following the funeral, Jenny trudges along a dusty road, singing to herself and talking to the collie that has begun to accompany her. The night air is pierced by the sight of a one-engine airplane on fire, crashing in the darkness, its fiery figure prompting Jenny to nickname it “Beelzebub.” A collie dog appears and starts walking with her, and a man drives up in a jeep—Dr. Steve Webster [Dean Jagger]—who offers Jenny and the dog a ride. He takes them to his home, where he shares the space with Murph [Walter Brennan], the local pharmacist. The morning after, Murph is surprised to find Jenny sleeping on the sofa with the dog, and the two residents learn that Steve is conducting research on Rocky Mountain spotted fever and has infected ticks on his porch. Steve is awaiting a grant that would let him teach and study at an institute in San Francisco, with a hopeful letter due any day now. Murph bathes Jenny and fills her in on the town’s backstories and some old-fashioned views on men, women, and marriage.
Steve invites Jenny to meet his friend Susan Moore [Ruth Warrick], who lives with Mathilda [Charlotte Greenwood]. Mathilda, who views Steve as a dreamer, warns that Susan would be foolish to wait for a proposal. Jenny, blunt and truthful from a life of isolation, speaks her mind about what she’s learned from Murph, which only angers Mathilda and leads Steve to remove Jenny and the dog from her sight. Later, Steve takes Jenny to Murph’s pharmacy for a sundae, but the nearby movie house draws a crowd of local kids. The ringleader is the mayor’s son, who torments Jenny. When Steve is away, the mayor arrives with a gun, threatening to shoot the dog. Steve ejects him, but the mayor trips on the porch, accidentally releasing ticks that carry the disease. Jenny is bitten, though Steve does not realize it. Sheriff Bolton [James Bell] arrives to arrest the dog, claiming it must await a trial, while Jenny’s fear grows that her canine companion might be destroyed.
Meanwhile, Clem Perkins falls ill with spotted fever, and his father laments that vaccination could have helped but never came. As the town’s parents begin to rush their children to Steve’s home for vaccination, Murph stocks up with vaccine from his pharmacy. Steve, who begins vaccinating Jenny, is interrupted before he can finish. The dog’s trial begins, with Murph stepping in as defense attorney in the absence of Steve. The mayor and his counsel contend that the dog bit the mayor’s son. Jenny testifies, but the judge initially rules the dog must be put down. Steve arrives and pushes for a medical examination of Blaine Perkins, the mayor’s son, to prove there were no injuries to the posterior. The judge reverses, but only to order the dog kept under observation in jail to ensure the animal isn’t diseased.
Jenny soon falls ill with spotted fever herself, and Steve admits that there’s little more to do beyond hope and prayer. News breaks of a plane crash involving a dog that had boarded the plane to Colorado to help create a serum by harnessing the dog’s recovered antibodies. The team surmises that Jenny’s dog is the same airplane dog, and with the institute in need of the correct dosage, they seek Dr. Nicholas Adams [Alan Napier], who is en route to Colorado. A radio emergency alert reaches Adams, who calls back with the precise dosage required to treat Jenny.
Dr. Adams arrives at breakfast the next day and awards Steve a $5,000 grant to continue his research on spotted fever. Steve announces his decision to stay in town, marry Susan [Ruth Warrick], and adopt Jenny [Natalie Wood]. The doctors have drawn enough blood from the dog to fulfill their needs and leave the canine for the future of the institute. Murph and Mathilda’s bond grows stronger, and the town finds itself on the path toward a hopeful future, with science, medicine, and community slowly healing its wounds. The film closes on a note of domestic happiness: Steve remains in the town, Jenny is cared for, Susan looks forward to a life together, and the patient dog is set to contribute in the broader effort to combat the fever.
