The Lone World. Ark Royal, #19

On her first deep-space mission, HMS Endeavour discovered two alien Dyson Spheres: one shattered, apparently nothing more than rubble orbiting a dying star; one seemingly intact, maintained by ancient super-technology so far advanced it may be beyond comprehension, inhabited by humans kidnapped from Earth hundreds of thousands of years ago.  Nearly trapped within the sphere, Endeavour barely escaped, leaving behind a disturbing mystery.  It is a mystery that must be solved - and quickly. Now, months later, a multinational task force is heading out to the spheres.  It's mission: to unravel the secrets of the alien technology, to determine who built the spheres and why and, perhaps most importantly, if they are still watching their creations, silently judging the visitors to their worlds.  But with the secret of super-tech up for grabs, and human nations and factions gambling everything on getting the tech first, everything hangs in the balance . .
And the spheres are waiting to see who'll be the first to take what they can for themselves.