Dyson Sphere (novel)

Summary
From the back cover: Two hundred million kilometers across, with a surface area that exceeds that of a quarter-billion worlds, the Dyson sphere is one of the most astounding discoveries the Federation has ever made. Now the U.S.S. Enterprise has returned to explore the awesome mysteries of the sphere. Intrigued by what is possibly the greatest archaeological treasure of all time, Captain Jean-Luc Picard hopes to discover the origin of humanoid life throughout the galaxy -- or perhaps the ultimate secret of the Borg.

But when a neutron star approaches on a collision course with the sphere, a mission of discovery becomes a desperate race against time. The many sentient species inhabiting the sphere face extinction -- can even the Starship Enterprise save them all?