Hunter loves exploring and asking questions. He's the kind of kid who always wants to know how everything works. One day his Grandpa tells him, “I love you." And, of course, Hunter immediately wants to know how much.

And so begins a quest for Grandpa to explain just how big his love for Hunter is.

Through many fanciful illustrations, Hunter learns how loud Grandpa's love is, how bright it shines, and how long it will last. But when they take a fall during a climb up a mountain, Hunter learns his most important lesson about how big Grandpa's love is.