When a vegetarian mother Maiasaura takes an abandoned dinosaur egg in with her own, she's surprised to have a Tyrannosaurus hatch beside her own little one. Naming him Heart, she raises him as her own. As he struggles to understand who he really is, Heart discovers his true heritage when he encounters another Tyrannosaurus while out picking berries one day. This startling encounter leaves Heart grappling with some major decisions about his future.