Space Dragons (Unabridged‪)‬

If Stan Pollux had known he would be spending his summer holidays in the outer reaches of our solar system, he would have put on different underpants. But when he gets kidnapped by the Planet Dragon Mercury, most things suddenly seem small and insignificant. Stan finds himself in a universe of dragons who had once ruled the skies as gods: Mars, Venus, Saturn, and even Uranus way out back. This is shaping up to be the best summer holiday in the history of the cosmos, until Stan discovers his stupid sister is missing, and that Pluto (AKA Hades) is trying to use her to destroy the Solar System. And it will be all Stan’s fault if he doesn’t get Poppy back.

So, all Stan has to do is learn how to fight like a hero in space armor, defeat the dragon god of the Underworld, Hades, rescue his sister, and save the world. All before his parents realize she is missing.