This one is hard to explain… seems to be a theme with Mr. Banks.
So many threads and themes. To boil it down, there is a 50-km-diameter sphere discovered off in the middle of nowhere. Is it a threat or opportunity?
One of the story-lines starts off with a sentient drone fighting for its survival as the enigma takes over its ship. The time-frame hops back and forth for many of the story lines.
In the vein of Fire upon the Deep, there are ‘verbatim’ formatted communications among the participants as they try to determine what’s happening based on limited information.