The skeleton of a plot.

In the near future, Earth discovers evidence of an alien civilization a few dozen light years away. Immediately, we make plans which include the creation of the Envoy, a large, gleaming, show-off kind of ship which will be packed with scientists, philosophers, and experts on human culture, as well as your generic shipboard necessities (doctor, cook, janitor, security, etc.), all under the command of Captain John Roland.

Something goes wrong. In a screw-up ultimately traceable to the rushed creation of the ship, it heads off in the wrong direction, and it can't be controlled or stopped. Someone comes up with a bright idea though; there are cryogenic pods stored with Earth perishables, plus some extras for emergencies and/or return visitors. It would be possible to cram a person in them, and fire them back at Earth. The frozen fellow would have a very slim chance of living, but the chances of living very long on the ship are utterly unknowable, so everyone agrees it's the best idea. Unfortunately, there is one person too many. Captain Roland valiantly agrees to be the remainder; the man who would go down with the ship.

Then, when it's down to the last two, he screws over the janitor, Aram Zlottowitz, and takes the last pod home.

Now, the Envoy moves very fast. Time dilation is in effect, and over the course of the next twenty years in Aram's personal time line, nearly two thousand very busy years pass for the rest of the universe.

The very aliens that Aram was sent to greet (or rather, clean up after the people who would greet), came to Earth. They had technology that could create wormholes between worlds. They freely shared the wormholes (if not the secrets of how they work). They helped us colonize a dozen or so Earth-like worlds. Then, their mothership got hit with frozen corpses from space. They got annoyed, and left, firing a few potshots at Earth, and closing their wormholes behind them.

Long, long later, we figure out how to re-open the wormholes. Enter the McNally, a tiny cartography ship, going through wormholes at random, mapping out the universe. One excursion, they get attacked by a colony that's turned a bit xenophobic, wind up going through an uncharted hole, and, with engines too damaged to make it back to Earth, stumble across the Envoy, in an erratic orbit around a neutron star.

The crew of the McNally successfully bolt the two ships together during one of the Envoy's slow turnarounds, patch the computers together and take control of the new combined ship. Of course, Aram is still there, and he claims captaincy. Now, they all have to get back to Earth through uncharted parts of the galaxy.

Hilarity, of course, ensues.