The Galactic Taxi Service

Take a few trips with the human race's only intra-star-system taxi driver as he ferries a varying collection of interstellar celebrities around and between the stars you see in the night sky: Sirius, Tau Ceti, Keid, Beta Hydri, Tabit and ultimately Deneb. The highlights include skiing down a mountain whose highest peak pokes out into space above the atmosphere, an expedition to hunt the apex predator in the most dangerous jungle in the known universe, a variety of ruins abandoned by nonhuman civilizations millions of years ago, and the most expensive birthday present ever conceived by the human mind.

Who built these abandoned cities, and how did they become embroiled in a far distant space war which shattered planetoids, casually flung inhabited planets to a distant frozen orbit, and melted deep craters into and through the planetary crust?

Follow a trail that starts at Saturn's moon Titan and leads finally to a ruined city whose inhabitants ruled this sector of a now-forgotten galactic empire. In the city, there remains behind a weapon, still functioning, that is capable of unimaginable destruction.

This technology was once used against Earth and could be again--this time by pirates of the future who have already harnessed alien technology for their own ends.

The question now is: How can an intergalactic taxi driver and an Oxford professor--with the help of a grumpy but brilliant artificial intelligence entity--prevent the pirates from securing the weapon and enslaving the human race?