Francesa Kinsolving, a very pregnant widow whose husband was rescently killed in action in Vietnam, travels to visit her late husband's mother in a snowy Minnesota town only to get snowed in during a fierce blizard where she's forced to wait it out only to slowly uncover some terrible dark secrets that Mrs. Kinsolving has been hiding, one of them is her psychotic other son, a recent escapee from a lunatic asylum, who is shacked up in the basement of the house.

After her air pilot husband Matthew is killed in Vietnam, young, pregnant Francesca Kinsolving takes a three-day bus trip through a driving snowstorm to stay with the mother-in-law she has never met. Despite Matthew's assurances her that she would get along very well with his mother, Francesca finds Mrs. Kinsolving cold and inhospitable upon her arrival at the grand, if gloomy, family mansion. Although determined to depart after her mother-in-law's unfriendly reception, Francesca is forced to spend the night due to the ferocity of the storm. That evening at dinner, served by Mrs. Kinsolving's mentally handicapped teenaged daughter Kathleen, who Francesca did not know existed, Matthew's mother declares she was never told of her son's marriage and is not interested in Francesca or her baby. That night after exploring her room, Francesca discovers a telegram from Matthew announcing their marriage and wonders why Mrs. Kinsolving has lied to her. Later, Kathleen brings Francesca a cup of cocoa and a newspaper clipping about her cousin Kenny, who is wanted for a vicious rape-murder. When Francesca awakens many hours later, she realizes that the cocoa was drugged. Still unable to depart because of the weather and now desperate to learn more about the family, Francesca investigates the library and discovers in the family Bible that Matthew's mother died eleven days after her son. Shock from this news sends Francesca into labor and Mrs. Kinsolving, a trained nurse, helps deliver a baby daughter, who she tells Kathleen, is stillborn. When Francesca has recovered slightly, Mrs. Kinsolving tells her that Kathleen has buried the infant, but later Kathleen secretly takes Francesca to the attic where she has hidden the healthy baby girl, and explains that Mrs. Kinsolving had mistakenly assumed the baby was stillborn. Soon after, Francesca is terrified to learn that Kenny is hiding in the mansion and wonders how she can remove her baby to safety. Through careful eavesdropping, Francesca soon learns that Mrs. Kinsolving is Matthew's aunt and Kathleen and Kenny's mother, and plans to drive Francesca away so that she might claim Matthew's inheritance. When Mrs. Kinsolving discovers that Francesca's baby is still alive, she tells Kenny that their plot has been discovered. The following day when the weather has cleared, Mrs. Kinsolving arranges for Francesca to get a ride to the bus from a mechanic, who is actually Kenny. Panicking, Francesca takes her baby and flees, with Kenny chasing her to the carriage house. Just as Kenny is about to attack Francesca, Kathleen intervenes, stabbing her brother in the back with a pair of scissors, sending Mrs. Kinsolving into deranged despair.