Eleven-year-old Sabrina knows the rhythm of her backyard by heart, but a "low and guttural" rumble from the treeline signals the end of her ordinary life. When she finds a "vast, impossibly large" footprint in the soft earth, she realizes something ancient has awakened. While the world remains oblivious to the "mountainous mound of matted fur" lurking just beyond the picket fence, Sabrina must face the terrifying truth: a giant sloth of legend has chosen her garden as its final refuge.