Cassi’s grandpa has dementia. Cassi doesn’t know what that means but she knows her grandpa can tell great stories and she loves when he teaches her to whistle and snap her fingers to a rhythm.
While playing hide and go seek, he wanders off, confused and lost. Cassi realizes he is gone and goes looking for him. Wandering through the forest she stumbles upon a giant house the shape of his head. Her grandmother is tending the garden outside and encourages her to go in and find him.
Through the house, she loses track of her grandpa and rediscovers him at different stages of his life, younger at each encounter. Cassi helps her grandpa escape old memories, scary events, and overcome inner fears.
Eventually she meets him at her age. The boy attempts to whistle but cannot. Cassi teaches him and suddenly realizes she has learned herself.
She says goodbye to the boy and runs back through the house whistling and finds her grandpa at his old age- and he laughs and whistles back. They rejoice and leave the old house back together again.