If you enjoyed Leviathan Wakes and can't wait to get your hands on Caliban's War, you can download James S. A. Corey's The Butcher of Anderson Station: A Story of The Expanse for 1.99$ here.
Here's the blurb:
A new story set in the world of The Expanse. One day, Colonel Fred Johnson will be hailed as a hero to the system. One day, he will meet a desperate man in possession of a stolen spaceship and a deadly secret and extend a hand of friendship. But long before he became the leader of the Outer Planets Alliance, Fred Johnson had a very different name. The Butcher of Anderson Station.