The story starts on the interstellar colony ramscoop Long Pass, bound for an unspecified world. The ship's navigator (having next to nothing else to do) discovers a sort of bow wave in the interstellar medium, and finds a planet at the apex of it--an earthlike world, frozen...and accelerating at about 0.001 G. Since it is not a natural feature of any planet to accelerate in interstellar space, they take it as a sign of intelligence and send a message laser in that direction, knowing it will take about a year for the message to get to the world. And on the night they are celebrating the message's arrival at the planet, they are attacked.
The story picks up with a young woman who is a pilot, flying a ship named Explorer, under the watchful eyes of a Pierson's Puppeteer named Nessus. She is a member of a three-man scout crew who is tasked with investigating potential threats to the Fleet of Worlds, which is composed of five planets in a Klemperer Rosette, fleeing the galactic core explosion.
Puppeteers are herd animals, herbivorous, and inveterate cowards, so they figured they (with their vast technology) were best served simply to move their worlds far enough from the galaxy that the radiation from the core explosion would be harmless to them. They already moved their world once, when their sun entered helium fusion and started swelling, so moving it a second time is relatively easy for them. Their homeworld is populated with a trillion Puppeteers, so it doesn't need a sun (their civilization's waste heat is sufficient to keep it warm) and they have chains of miniature suns to keep their three (and then four) "Nature Preserve" worlds lit, warm, and fertile, and those worlds are where they grow the food needed to support a trillion herbivores.
("Crowding"? Why would crowding bother a herd animal?)
I say "and then four" because the mystery planet at the beginning of the story turns out to have been added to the rosette relatively recently.
And things get better from there.
Anyway, I first picked this series up in the middle, and years ago--I think when Mom was still alive, in fact--and liked it. Juggler of Worlds was the first one, I think, and then a while later I got Fate of Worlds, reading everything out of sequence. Last night I got Fleet of Worlds and Betrayer of Worlds.
Fleet of Worlds...and I'm not sure if there's another one, or not.
Juggler of Worlds
Destroyer of Worlds
Betrayer of Worlds
Fate of Worlds
What kept me from getting more of these books prior to last night was that I couldn't remember which ones I already had. The bookstore is far enough from the bunker that I don't want to have to make a special trip there if I don't have to, and taking a book back would be just such an annoyance. But I checked before we left yesterday, and made sure to note which ones I had, so I could select one or two with impunity.
I was certain that I had three of the books, but I could only find two. Since I'm going through Fate about as fast as grease through a goose (I have perhaps 20% left to read after starting after 9 PM last night) I expect to begin reading Betrayer sometime today, and I ought to know pretty quickly if I've read it or not. I don't think I have. WTF, if it turns out that I have another copy somewhere but I can't find it and don't remember reading the story, is the money really wasted?
I was also looking over Destroyer and didn't recall anything from that one--and Louis Wu makes an appearance there, which I am pretty confident I would remember. (Of Niven's recurring characters, Louis Wu and Beowulf Schaeffer are the best, IMHO, because Niven reserves his best stories for them.)
But I was already holding two books, and I had to make a decision, and finally I went with Betrayer because it refers to a Pak library, and whenever the Pak get involved things invariably get really interesting, fast. And since I started reading this series out of order, it's not important that I read them in order. (And the books are written to stand alone fairly well, anyway.)
This is a good series. It's hard SF, not "pink" SF, and it's about people doing interesting things in space with aliens that are convincingly alien. I'm enjoying it.