On a dark and stormy night, Meg Murry tosses and turns in her attic bedroom. She is unable to fall asleep because she is preoccupied with all that seems wrong in her life: she doesn't fit in at school; her high school teachers have just threatened to drop her down a grade on account of her poor academic performance; and worst of all, her father has been missing for many years and no one has heard from him. Meg hears her family's big black dog Fortinbras barking downstairs, and she begins to worry that a stranger may be skulking around the house; she suspects the tramp who, according to local gossip, recently stole twelve bed-sheets from the constable's wife, Mrs. Buncombe.
Dismissing her fears as silly and attempting to calm her nerves, Meg decides to make herself some cocoa in the kitchen. She is surprised to find her five-year-old brother Charles Wallace waiting for her at the kitchen table, though she notes that Charles always seems capable of reading her mind. Mrs. Murry soon joins her children, and tells Meg that she has received a call from Mrs. Henderson, the mother of the boy Meg had beaten up at school that day. Meg complains to her mother that she hates being an "oddball" at school. She wishes she were more ordinary like her twin younger brothers, Sandy and Dennys. Mrs. Murry tells Meg that she needs to learn the meaning of moderation, the importance of finding a "happy medium." Charles then comments that he has spoken about Meg's problems with his friend Mrs. Whatsit, though he refuses to explain who this woman is.
As Charles Wallace is preparing sandwiches for his mother and sister, Fortinbras begins to bark loudly again. Mrs. Murry goes outside to find the cause of the commotion. She returns with Charles's mysterious friend Mrs. Whatsit, an eccentric tramp completely bundled up in wet clothes. Mrs. Whatsit explains that she glories in nights of such wild weather, but that tonight she has been blown off course in the storm. Charles asks her why she stole bed-sheets from Mrs. Buncombe, confirming Meg's suspicion that Mrs. Whatsit is the neighborhood tramp. After removing her boots and drying her feet, Mrs. Whatsit suddenly remarks that "there is such a thing as a tesseract" and then hurries out the door. Mrs. Murry stands very still at the threshold, stunned by Mrs. Whatsit's parting words.