Walter, Ashley, and Karen ride the dragon Thigocia in search of her son, Gabriel. When they find an army of giants hibernating in the depths of the earth, they meet a mysterious girl named Sapphira Adi who claims to be thousands of years old. Sapphira reveals a sinister plot. The giants will soon awaken and rise to conquer and destroy, and only dragons can defeat them. Since only two dragons remain on the earth, and one of them is reluctant to fight, doom seems certain. With Excalibur at his side, Walter plunges into an ancient world to find a mysterious ally who could help them save the world.
