This starts off as a Film Noir in space, more than anything else, with detective/policeman Joe Miller (Thomas Jane) investigating the disappearance of a young woman. It's two hundred or so years in the future and mankind has colonized not only the moon and Mars but the asteroid belt. There's also the story of Jim Holden (Steven Strait) who, along with a disparate group of characters, ends up salvaging a Martian spaceship. Oh, and there's the complicated politics of Earth and the planets, which teeters on war. Holden and his crew uncover an experiment that involves a "proto-molecule" and this is viewed as a threat, a weapon and even the next step in mankind's evolution. Eventually the crew encounters Joe Miller and they team up to uncover the conspiracy and to deal with the threat.
THE EXPANSE is a very complicated series, with well-defined characters and an intriguing story. If you miss one episode you'd probably be hopelessly lost as to what's happening. The special effects are also great, akin to the recent BATTLESTAR GALACTICA series. If you like space shows then you'll love this. Highly recommended.