This is another in Iain M. Banks' series of sci-fi novels set in the 'Culture' universe. It's about a professional games player, a man who's immersed himself in games as a lifestyle as much as a livelihood. He finds himself adrift in life, unable to attract the attention of the woman he's interested in, losing interest in the games he's playing, and generally not having very much fun, anymore.
Then an acquaintance (a disgraced military robot) blackmails him into accepting an offer from the government (such as it is) and he heads off on a mission to explore a foreign galactic empire that actually organizes itself on the outcome of a complex game played by its elite. He's dipped into the first truly high-stakes game of his life, and more or less gets what he wanted (which we all know is a bad thing).
It's a long read, and fairly demanding, but Banks manages to convey a rich impression of a sinister future for mankind that's quite unique. I look forward to finding more of the same by this author.