9Kid inventors Nick and Tesla Holt have outsmarted crooks, spies, and kidnappers. Now they have to crack their biggest mystery yet: Where the heck are their parents? To outwit the criminal mastermind who's holding their parents hostage, the twins will need all their brainpower, the help of their eccentric Uncle Newt, and an assortment of homemade solar gadgets. Will the Holt family be reunited at last? Or will a hijacked solar satellite beam down doom from the skies? The adventure includes instructions for creating a solar-powered hot-dog cooker, alarm, secret listening device, and model car, plus a nighttime signal cannon that fires illuminated ping-pong balls.