The Double Deckers subversively defend their den from being taken over by the local council who want to convert it to a car park. The mayor makes an inspection of the property along with the council with hilarious results - it appears to be haunted. But we know who the little goblins are. When Billie is paid 2 pounds a week for watching Scratch the dog, the gang realizes the potential for riches and set off to make the place fit to board lots of animals. The only taker is a flea trainer who is looking for a place to keep his fleas after he was kicked out of his flat for having them.
Scratch runs away and the kids are sad.
To cheer everyone up, the flea trainer shows the flea circus. When the kids return the dog, the landlord is so pleased that the flea trainer is asked to move back to the flat. And the kids find a new use for Brains' radio signal - finding and returning lost pets for profit. Billie and Tiger are upset the boys aren't paying any attention to them. Realizing this, the teacher fakes a hurt ankle so the girls will be in the show.