If we consider Invincible the eighth book in The Lost Fleet series, it is the best of the series so far. It has practically none of those pages where the author reminded us of things we already knew, instead the book is packed with new discoveries, new challenges, new opportunities, and even some humor. None of the previous books contain nearly so much action or so many surprises.
Precisely because the book is so much more content-heavy than the other it requires more attention. The other books were almost invariably structured by chapters with roughly one star system adventure by chapter. New chapter, new star system, new adventure. But now things are starting to spill over star systems, we get a wider picture and some stories continue through the jump gates.
In Dreadnaught, the Alliance Council had ordered Admiral Geary to take his mighty fleet beyond the Syndic Worlds to explore the space occupied by the Enigma Race. But Geary had to know how big the Enigma space was so he went beyond it, only to stumble into another unknown alien race by the end of the book.
Invincible begins with the aftermath of that first encounter with the second alien race. But instead of just defending their systems like the Syndics and the Enigma used to do, this new fleet follows the protagonists deeper into unknown space. Every step they take in this Terra Incognita reveals some new surprise. The author has finally decided that we are familiar enough with the Lost Fleet world and feels ready to really speed things up. And Campbell improves with velocity.
Just in terms of aliens we get much more in Invincible than in all the previous books combined. But then there is so much more. This time, Campbell reveals some cruel practices that the Alliance had resorted to during the war and how the victims are still trying to learn to cope with all that. The particular victim in this story is an officer that deeply resents Geary. The Admiral, of course, wants to help the poor man but how can he? In typical believer fashion, Campbell always leaves some room for hope.
And so, despite such sad stories and despite the new enemies and unresolved troubles, the book feels brighter and more light-hearted; the long war against the Syndics is over after all and the crew seems to be relearning to relax a bit and have a few laughs. Campbell even has a character joking about the cover art and a funny story about a 20th century human technology that aliens covet. Even the description of the second alien race is decidedly humoristic.
And then, the fleet has to head back to Syndic space where Campbell keeps planting seeds for new books. It looks like the story here will bifurcate with some books telling us more about the post-war Syndic Worlds and some other book following Geary and company.