Zoé, Lassie et Harvey sont avec Graham en ville quand Sarah les appelle en urgence : madame Lee a été mordue par une araignée venimeuse et a besoin au plus vite d'un antivenin...
Joe Carraclough lives with his parents and his dog Lassie in a small town in Yorkshire, England. Lassie and Joe are inseparable. Because they are poor, Joe's father has to sell the dog. But Lassie escapes and returns to the Carracloughs. That's why her new owner takes her to his estate in Scotland. But she also runs away from there.