Originally Francoeur was a miniscule flea living peacefully on the back of Charles, the monkey who assists the botanist at the Zoological Gardens. During a reckless experiment, however, Raoul turns him into a gigantic 2-meter tall flea! Who soon strikes terror into the citizens of Paris, causing Commissioner Maynott to come gunning for him. Françoeur conceals his monstrous appearance behind a wonderful singing voice and a heart of gold.