In a fantastical world of horses, swords, and treasure, young Hesta lives a normal life, along with her brother Thane. One day, though, she makes an incredible discovery. She comes upon a creature the size of a fawn with two tiny wings folded against its back and a long pointed tail. In its talons, it holds a green jewel that sparkles in the darkness of a ravine. Hesta has found a baby wyvern – a poisonous dragon with two legs and giant wings. The discovery is indeed amazing, but it soon turns dangerous when Thane ends up poisoned after the parent wyvern finds and attacks them. Desperate to save her brother, Hesta takes on several risky missions to find the cure for Thane's illness. Everyone now seeks the wyvern's green jewel, including a treasure hunter named Nordore. Along with their faithful horses, a mysterious man, and a clever cat, this brother and sister race to save not only themselves but also the magic of the wyvern.