In a laboratory, Hempy, a mouse who is the perfect example of aversion to change, is part of an experiment. He lives a completely routine life, down to the millimetre and to the second, just as he used to live it with his wife, although now he can only remember it. One day, however, another mouse is added to the cage, and from then on everything starts to change little by little: the temperature cycles, the inclination of the cage, the amount of food, and even a snake is introduced into the habitat! Will Hempy manage to give up his comfort zone and follow the new mouse?