[CRussel]

I'll nominate Agent of Change, one of the gateway books to the Liaden Universe. This is available as a free book from:
Amazon
BaenEbooks.com
Kobo

The Audible version isn't free, but is WhisperSync enabled: Audible )

The Liaden Universe is a complex universe spanning millenia, and is multi-threaded. There are lots of entry points into it, but this is the most obvious one, since it is the first book published. The Liaden Universe books are character-driven books with a healthy dose of world building over time. They are not "shoot 'em ups", though we certainly get some action in this one. They are also not "hard science" books, but probably fit into "space opera" as much as anything else. They are about cultures and their interactions, since we have three main "species" - humans, Liadens, and Yxtrang. Oh, plus Clutch Turtles who appear here and there.

The Amazon description for this book is:

Spoiler:

Once a brilliant First-in Scout, Val Con yos'Phelium was "recruited" by the mysterious Liaden Department of Interior and brainwashed into an Agent of Change—a ruthless covert operative who kills without remorse.

Fleeing the scene of his latest murderous mission, he finds himself saving the life of ex-mercenary Miri Robertson, a tough Terran on the run from a team of interplanetary assassins. Thrown together by circumstances, Val Con and Miri struggle to elude their enemies and stay alive without slaying each other—or surrendering to the unexpected passion that flares between them.

I highly recommend the books of Lee and Miller, and think this is an excellent entry into the Liaden Universe. And it's FREE.