Eleven-year-old Mabel Cunningham is a quiet loner who only feels free to be herself when she's "extreme treasure hunting" with her grampa--much to her perfectionist mother's disapproval. Nothing excites Mabel more than discovering a heart find, an item that calls to her heart, and the maybes that come along with it.

But when her friendships start to crumble and her grampa suffers a stroke, Mabel quickly learns that real-life maybes are harder to handle than imagined ones. Desperate to change things back to the way they were, Mabel devises a plan that she believes will fix everything. Except bringing her plan to fruition means lying to her grampa and disappointing her mother.

Will Mabel learn that letting go of the past doesn't mean letting go of her grampa and that embracing the future might be one of her most important heart finds yet?