Deep in the heart of children's imagination lies the land of , where trains have come to life and everything runs on rails. The 'Chuggers' in this magical world are all based on modern engines of every kind, from stream-lined diesel locomotives and electric bullet trains to trolleys and old steam engines. Three apprentice engines (called 'trainees' of course!) are learning to ride the rails and perform essential tasks - Wilson (an eager but slightly impetuous red engine), Brewster (a loyal and rugged freight engine) and Koko (whose speed and daring deeds sometimes get her into mischief).