In a dark and eerie laboratory, the mad scientist Mickey (voiced by Walt Disney) is cultivating a mysterious potion. This concoction is brewed with various highly toxic, terrifying, and dangerous drugs, yet it possesses the powerful effect of enhancing courage. After completing the preparation, Mickey decides to test the potion's efficacy. He pours it onto a small fly trapped in a spiderweb. A miracle occurs: the once trembling fly gains immense courage, defeats the much larger spider, and successfully escapes. Following this, he sprays the potion on a mouse being chased by a kitten, and the little mouse stages a spectacular counterattack.