Rose Cottage is the home of a human family: Mr Walter Mildew and his children, Arthur and Lucy.

Mr Mildew is an inventor and is struggling to maintain the family while he develops his latest invention, a mechanical mouse that cleans.

Due to their father's absent-mindedness and financial situation, Rose Cottage is in poor repair and Arthur and Lucy wear threadbare clothes and are frequently hungry.

In desperation Nutmeg enlists the help of General Marchmouse, a recently retired member of the mouse army.

Marchmouse, with much unacknowledged help from Nutmeg, formulates a plan to drive Ivy from the house via a massed charge of the village mice.