In a Scottish and picturesque region, a young man named Angus discovers a mysterious egg while exploring the shores of a lake. Intrigued by his find, he decides to take it home, only to discover that an extraordinary creature emerges from it: an adorable and charming being that resembles a small aquatic dinosaur. As the creature grows, Angus names it 'Crusoe,' and their bond strengthens. However, the young man soon must face the harsh reality of keeping his friend a secret, for the outside world is not prepared for the magic that Crusoe represents.
As World War II breaks out, the story takes an unexpected turn when tension and fear impact Angus and his family's lives. The threat of soldiers and the pursuit of an unknown enemy loom over the small town, bringing forth both the courage and loyalty that have developed between Angus and his magical creature. What begins as a simple friendship transforms into a grand adventure in which Angus must protect Crusoe from those who do not understand its nature, thus becoming the guardian of a legend that transcends time. The story is a poignant journey about love, bravery, and the connection between nature and humanity, all while challenging the forces that seek to separate them.