Larry Niven & Edward M. Lerner – Fleet of Worlds

Kirsten Quinn-Kovacs is among the best and brightest of her people. She gratefully serves the gentle race that rescued her ancestors from a dying starship, gave them a world, and nurtures them still. If only the Citizens knew where Kirsten's people came from…
A chain reaction of supernovae at the galaxy's core has unleashed a wave of lethal radiation that will sterilize the galaxy. The Citizens flee, taking their planets, the Fleet of Worlds, with them.

For too long, the Puppeteers have controlled the fate of worlds. Now Sigmund is pulling the strings...
Covert agent Sigmund Ausfaller is Earth's secret weapon, humanity's best defense against all conspiracies, real and potential - and imaginary - of foes both human and alien. Who better than a brilliant paranoid to expose the devious plots of others?

The brilliant, xenophobic Pak are fleeing the chain reaction of supernovae at the galaxy’s core. Nothing and no one is going to impede their migration. Devastated worlds -- any civilization that could possibly have interfered -- lie shattered in their wake. And now the Fleet of Worlds is in their sights.
The trillion Puppeteers who inhabit the Fleet might have the resources to confront the threat -- but Puppeteers are philosophical cowards. They don't confront anyone. They need allies to investigate the situation and then take action. Who better than the Puppeteers' newly independent one-time slave world, New Terra?

Fleeing the supernova chain reaction at the galactic core, the cowardly Puppeteers of the Fleet of Worlds have---just barely---survived. They’ve stumbled from one crisis to the next: The rebellion of their human slaves. The relentless questing of the species of Known Space. The spectacular rise of the starfish-like Gw’oth. The onslaught of the genocidal Pak.
Catastrophe looms again as past crises return---and converge. Who can possibly save the Fleet of Worlds from its greatest peril yet?