Green for Danger (Teen Power Inc., #6)

Minding a luxurious house seemed like fun to the Teen Power gang at first. But now Nick is feeling more and more uncomfortable. Suddenly the house seems like a prison. Or a tomb. Is it the sealed windows and doors? Or the aquarium fish swimming in endless circles? Or maybe it's just that a fortune in emeralds was stolen from the house, ruining its owner, and disappearing without a trace...