Nautilus (Starfarers #4)

The death of her cherished friend and guide Nemo, the alien squidmoth, came as a crushing blow to J.D. Sauvage. But J.D. and the first contact crew of the Earth ship Starfarer hope that the enigmatic being's legacy - the starship Nautilus - will lead them closer to communion with alien intelligence. Awaiting them on their journey are the representatives of the Four Worlds and one last chance to join interstellar Civilization, from which Earth has long been barred.

But first J.D. and her fellow wayfarers must convince the aliens that humanity is worthy of Civilization. It is an argument that they will find hard to win, given humanity's violent past. What's worse, they don't have much time to win it. For the cosmic string that can guide the Starfarer home is fast unraveling. Soon the beleagured crew will have to make a decision that will affect all the people of Earth: whether to turn back to Earth while there's still time - or make one last desperate effort to win over their implacable alien hosts.