A lonely boy, struggling with the loss of his father, discovers a mysterious egg, which soon hatches a sea creature of Scottish legend, the Water Horse. The boy, named Connor, forms a special bond with the creature, keeping it a secret from his mother and grandmother. However, the Water Horse grows rapidly and attracts attention, as Connor struggles to find a way to hide his secret companion. As they embark on an adventurous journey, a shocking discovery reveals a greater threat to their unusual friendship.