“You have to play the game in real time,” between episodes of the series, “to get the fullest experience,” said Kevin Murphy, an executive producer for the show.

Considered separately, the television series and the game aren’t all that interesting. “Defiance,” judged by its two-hour pilot and the second and third episodes, is an entertaining trifle set in the near-future St. Louis after an alien invasion. It’s the science-fiction version of an Old West frontier show, with brothels and a sheriff (called the “lawkeeper”).

There’s Joshua Nolan, a Han Solo-like scoundrel with a heart of gold, played by Grant Bowler. One of the seven alien races appears to be some kind of orangutan Chewbacca. A motorcycle gang garbs itself in the standard post-apocalyptic attire of seemingly mismatched athletic apparel — a catcher’s mask, perhaps, or half of a set of football shoulder pads. The gang leader sports a top hat with goggles, giving him the appearance of one of the Dothraki from “Game of Thrones” who chose the life of a steampunk vaudevillian. There are interspecies love affairs, an alien albino mob boss and a lot of weird contact lenses. It’s joyfully derivative and better than it deserves to be.

The first several hours of Defiance the game, a massively multiplayer online world set in the same universe’s San Francisco, are less entertaining. Running around and shooting things — bugs and mutants and whatnot — is reasonably fun, but the character animations, acting and dialogue all feel second class. A lot of the game is discontinuous, with scenes beginning and ending abruptly, and a little buggy, at least on the Xbox 360 version that I played. (It is also available on PlayStation 3 and on personal computers.) It’s too early to give up on the game — one of the benefits of a big virtual world like this is that it can be altered and improved over time. As an isolated experience, though, it’s not worth checking out yet.