A child on a walk discovers a small line lying on the path. Machinically, he puts it in his pocket and forgets about it. But the line is alive! This is the beginning of a long adventure together. The little line grows with the child and becomes his friend, taking on all sorts of shapes and translating the rich palette of life's emotions. It is magical! And if it is sometimes mischievious, sulks or hides, it also helps him, encourages him, saves him, surprises him and makes him laugh...