Eight-year-old Francesca "Frankie" meets George Saint James on the day her mother disappears. After waking to a spring rain and noticing their mother's station wagon is gone, Frankie and her brothers ask their father what happened. Their father, distracted and withdrawn, says their mother has "gone home" and promises she will return, though only Darwin seems to grasp the meaning.

With no real explanation and no comfort, Frankie, Darwin, and Moby are sent outside. Frankie feels neglected by her brothers when they exclude her from their basketball game, so she looks for her own entertainment with a butterfly net. What begins as a childish hunt for a frog or insect turns into something more compelling when she spots a rabbit and chases it across the field.

The chase leads Frankie to a gap in the cedar hedge bordering the neighboring property, the imposing "Big House" she believes belongs to a witch. There she finds a pale, shy boy watching her from the other side. Frankie introduces herself boldly, and the boy says his name is George and that he now lives in the Big House with his grandmother.

Frankie insists George's grandmother must be a witch, repeating neighborhood lore about her appearance and house, and challenges George to prove otherwise by letting her inside. George denies anything magical is there, though he offers the enticing detail of a black cat named Baryshnikov. Excited by the chance for the adventure she has been craving, Frankie asks to see the house, and George invites her in. Frankie follows him into the Big House, marking the beginning of a life-changing bond for both of them.