The Shield family's ordinary summer holiday takes a dramatic turn when Calum, the imaginative middle child, sculpts a dragon from the beach's sands. Goaded by a mysterious woman's voice preying on his hurt and anger, he inserts a strange black ammonite fossil into the creature's eye socket, unwittingly awakening an ancient dark power.

Calum and his brothers, Jake and Adam, face a race against time to save themselves, their parents and Calum's twin sister, Amy.

As the boys attempt to undo what has been set in motion they embark on a dangerous journey which will force them to sail alone across treacherous waters, explore the dragon's lair deep within a cave, outwit a growing ancient force bent on destruction, and battle to the death against an immortal foe.

Together, the boys must explore sibling rivalry, forgiveness, family loyalty, and redemption as they grow from squabbling brothers into courageous heroes facing impossible odds.