Feeling "cooped up" and tired of living under the strict discipline of her parents and grandmother, 10-year-old Winnie Foster decides to run away from home. When she ventures out on her own, she discovers a young man in her family's wood who belongs to a remarkable family with a remarkable claim: that the water from a spring in the forest has blessed (or cursed) them with immortality.
Mae Tuck, the family's matriarch, kidnaps Winnie in order to keep this secret safe, but the stranger in the yellow suit is already on the Tucks' trail, eager to exploit their secret for his own financial gain. Is eternal life a blessing or a curse?
Winnie must decide whether she believes the Tucks' claim, if she will trust and help them, and—before her adventures end—whether or not to join them on their never-ending journey.