Fromage dreams of following in her family's pawsteps as a shipboard rat-catcher, but her Mama Cat insists that such work is hardly suitable for a proper young lady. Undeterred, Fromage sets off on her own adventure-only to befriend an orphaned Scottish rat named Aloysius, much to her mother's dismay.

Fortunately, Papa Cat is more understanding. He enlists a spirited young lad named D'Artagnan to train the unlikely pair in the art of sword fighting. Their skills are soon put to the test as they journey to meet the Queen of France, encountering a mischievous mermaid and a band of robbers along the way. It will take all their courage, cleverness, and swordplay to make it through unscathed.