On the shores of Loch Ness, Angus stumbles upon a strange, pulsating egg. Curiosity compels him to take it home, where it hatches into a creature unlike any he's ever seen: a tiny water horse. Angus names him Crusoe and secretly hides him in the barn, nurturing him as he grows rapidly.
Angus and Crusoe forge a deep bond, exploring the loch and playing amidst the Scottish countryside. Their idyllic world is threatened by the ever-present shadow of war and Angus' longing for his father, lost at sea. To keep Crusoe safe, Angus must hide him from his strict mother and the prying eyes of others, creating a web of secrets and anxieties.
As Crusoe grows bigger, whispers of the legendary Loch Ness Monster begin to swirl. Scientists and military officials descend upon the loch, determined to capture the elusive creature. Angus faces a terrible dilemma: protect his beloved friend from those who would exploit him or reveal Crusoe to the world and risk endangering him.