Topper finds himself bored during the summer break, longing for his father who is off exploring the world’s oceans. He is also puzzled by Sille, who he finds charming. Meanwhile, his closest friend, Viggo, is often busy assisting his meticulous father, Mr. Lion, in the café located on the ground floor of the red building where Topper resides with his mother on the top floor. Everything changes when Topper discovers a magical pencil and sketches a rhino on the wall, which astonishingly springs to life! As Topper and Viggo strive to keep the rhino, whom they name Otto, satisfied with black bread and raspberry soda to prevent it from munching on all the furniture, Mr. Lion urgently appeals to the local authorities to deal with the rampaging creature.