Frank Adler (Chris Evans) is a single man raising a child prodigy - his spirited young niece Mary (Mckenna Grace) - in a coastal town in Florida. Frank's plans for a normal school life for Mary are foiled when the 7-year-old's mathematical abilities come to the attention of Frank's formidable mother, Evelyn (Lindsay Duncan), whose plans for her granddaughter threaten to separate Frank and Mary.