Another collaborative prequel (Fleet of Worlds, 2007) to Niven's enduringly popular Ringworld yarns.
Amalgamated Regional Militia agent Sigmund Ausfaller, a genius and certified paranoid, labors in the shadowy world of intelligence, keeping Earth and its colonies safe against alien threats. Surprisingly, it’s the cowardly, herd-minded Puppeteers that currently represent the greatest danger, since they're obsessed with protecting their species against every conceivable threat, both real and imaginary. General Products, the Puppeteers' commercial arm, sells spaceship hulls that are guaranteed indestructible and proof against all known radiation. So when a scientific vessel turns up with its hull intact but the contents (including crew) mangled almost beyond recognition, Sigmund must find out what happened (it turns out the ship strayed too near a neutron star and was shredded by intense gravity). Meanwhile, the Puppeteers are selling advanced technology to selected individuals, subverting others, spying on everybody—until they discover that the galactic core is exploding. And although they won't be affected for thousands of years, they choose to take immediate action, and all Puppeteers vanish—save for a select few hardy scouts like Nessus, who continue to pull strings to their own mysterious ends. All Sigmund has to do is figure out what and why.
The book's first half rehashes, from another point of view, several of Niven's Known Space stories from way back, and the rest isn't much better: slow-turning wheels within wheels within wheels.