In the story, a boy named Nicholas is punished by his strict aunt for putting a frog in his bowl of bread-and-milk at breakfast. He is grounded while his brother and their cousins go out on an afternoon excursion. As further punishment, he is told to stay out of the gooseberry garden. Convinced that Nicholas will disobey her, the aunt puts herself on sentry duty in the garden. Nicholas, however, has a better plan for the afternoon. He intends to sneak into the mysterious lumber room which is always kept locked.