While Mary and Laura are playing in the yard, Laura is beside herself when she falls and breaks her doll, Janet. Charles attempts to patch the doll but it is hopeless. Some of the broken pieces are as small as pieces of dust, and unfortunately, he and Caroline can't afford to buy another doll. Mary, feeling guilty, tries to buy a doll's head at the Mercantile with her own money, but they are too expensive. On the way home, she finds a baby raccoon so she gives it to Laura who names him Jasper. Charles is adamant about not letting Laura keep the pet but eventually he gives in, though he makes her keep Jasper in the barn.
Laura teaches Jasper to stand up and beg. As Laura takes Jasper to school to show the kids, Jack shows his jealousy. At school, Jasper's a hit with the kids. Laura tells the kids that Jasper never bites. As they get ready for church, Laura teaches Jasper a new trick: hiding his eyes. While the family is at church, Jasper terrorizes the chickens and Jack chases him into the house where he causes all kinds of mischief. Charles decides to take Jasper to the woods and release him. Returning to the barn later, Charles finds Jasper has returned, to the delight of Laura. So Charles builds him a cage. When Laura tries to feed Jasper in his cage, Jack makes such as fuss that Jasper bites Laura. Escaping his cage, he gets into a fight with Jack, bites him too and runs away. Laura swears Mary to secrecy about the bite.
Charles tries to console Laura on the loss of Jasper but Laura blames Jack. Mary spills the beans about Jasper biting Jack. Later that night, Jasper raids the hen house causing a ruckus. Charles goes out to investigate, he finds dead chickens and Jasper and kills him. Later he apologizes to Laura but she blames herself for feeding him eggs. Later, Caroline visits the barn where Charles has Jack tied up. He tells her that the raccoon was rabid and that it had bitten Jack earlier so he might become rabid, too. The next morning, Mary is gathering the eggs when she sees Jack tied up in the barn. She starts to untie him when Pa stops her. He tells her that Jack might be rabid. She tearfully tells him that Jasper also bit Laura.
They take Laura to see Doc Baker and he examines the wound. He gives her a gumdrop as medicine. When she goes outside, he tells her folks that rabies runs its course in a dog in 8 days. In a human, the incubation period is 3 weeks to a month. Caroline is shocked to find out that there is no treatment for rabies. Laura asks her mother what is going to happen to her but Caroline lies. She presses Pa and he finally tells her that she might get sick. Charles feeds Jack but everyone is on pins and needles. In the barn, Jack's barking gets more frantic, then he quiets down.
In the loft, Mary asks Laura if she hates her. She blames herself for giving Laura Jasper and for not telling him when Laura was bitten. Laura reassures her and expresses her love. When Mary tells her mother that Laura is thirsty, Caroline panics. As Charles is giving her some water, Jack begins barking again. Everyone realizes what this means. Charles gets his rifle, loads it and heads for the barn, telling the girls to stay in the loft. Just as Charles is about to kill Jack, he quiets down and starts whining. Suddenly, a raccoon drops down on a nearby bale of hay. It stands on its hind legs and covers its eyes. It's Jasper! Charles realizes that the rabid raccoon he had killed earlier was not Jasper and he runs into the house to tell everyone. Laura runs to the barn and unties a very happy Jack.