On a second reading, this book really grew on me.
The book opens with Chromis Pasqueflower Bowerbird attempting to get her government to create a memorial to the Benefactor - the person behind mankind's spread to the stars - as the 10,000 year anniversary for the founding. Apparently, the Benefactor is one Bella Lind.
The basic set up is that the comet 'mining' vessel Rockhopper is the only ship that can intercept Janus, a moon of Saturn, when it starts moving out of the Solar System under its own power. China mounts a risky rival expedition to also intercept. Along for the ride are the entire crew of Rockhopper, which is where it starts getting interesting.
The captain, Bella Lind, and her engineer, Svetlana Barseghian are friends and this makes things complicated later. Due to an accident, there is evidence that the ground control is fiddling with their data - that there may not be enough fuel to make it home. Add in that Janus has quite a few surprises in store as well, other people with conflicting agendas and goals and you've a very interesting story.
I'll spoil this much - the story involves relativity, deep time, an answer to the Fermi Paradox, aliens, human relations, politics, vendetta, revenge and ultimately atonement. Its a pretty good read - I think one of Reynolds' better works and one I'll read again some day (after I've cleared my shelves of to be read books).
Good first contact story. It got a little bogged down in places but I managed to finish it. I'd recommend this book.