Mass Effect is a trilogy of games, two of which have so far been released with a third due in 2012. Humanity has just recently joined the greater galactic civilization where humans are regarded with great suspicion. In the games, players can create their character (male or female, good or bad) and guide the story along various paths, whether saving or destroying species, individuals, etc. with the ultimate goal of saving the galaxy from an ancient threat. While this is the general plot, it is impossible to exsplain more; player chocie have major impact on the storyline. Knowledge of the games isn't necessary, but it is the draw to these books.

The first book, Mass Effect : Revelations, is a prequel featuring some of the background characters and the villain of the first game, but is largely a new cast with a stand-alone adventure that sets up the plot of the rest of the game series.

The second, Ascension, is even more independent, but is set between the first two games: while the universe is the same, there isn't a direct link to the action in the games. What is interesting though is the lengths the author has to go to to avoid mention plot points, as the game has several, very different, endings. The third and upcoming later books in the series will follow the same formula, sharing the universe with the games, but not being directly tied to them.

The writing isn't very good, but quality writing isn't the point. It's an expansion of a universe, sort of like Star Wars novels. In this case, the author also happens to be the lead writer for the games, so there aren't any many major contradictions with the games.