Pascal is spending a holiday in Portugal with two other French children called Richard and Mariane. They are staying at a working farm owned by José and Theresa Costa near to a fishing village on the coast. Pascal's horse, Poly arrives on a boat from France to join them, but promptly disappears into the local countryside. Poly soon reappears and leads the children to a wanted man on the run who claims to be searching for his missing son. With the aid of Poly, a fisherman called Faustino and the village children, Pascal, Richard and Mariane set out to solve the mystery. They are constantly hindered by inflexible village policeman Bernardo, who prefers to follow regulations to the letter at all times.