Lilith, the name is important for the reference, awakens on an alien ship, long after the human race has almost destroyed itself (doomsday). The problem is that in order for the human race to continue live, Lilith must work with aliens who will make the humans a bit more than human.
The book is more internal driven - the conflict, at least for the first part of the book - is whether or not Lilith will work with the aliens. What Butler captures well in the book is the conflicting desires a person has as well as the conflicting loyalties. When more people are awaken, things get more difficult.
While the book is somewhat bleak, it is also very real. In part, this is because Lilith is such a wonderfully designed character. Her internal conflict and emotions are shown very well, and the questions that the book raises are interesting and important.