Essentially, a naive overly optimistic girl gets a post card in the mail inviting her to a game called The Liar Game. Unfortunately, 100,000,000 Million Yen was also mailed to her, and once she saw the money, it confirmed her spot in the game.
The objective of the game is to steal your opponent's 100mil ($1 million USD). At the end of a month, if you don't have your million, you'll be forced into a 100,000,000 Yen debt for the rest of your life.
So the girl enlists a con-man genius to help her. With his help, they tackle all the obstacles the company behind the game throws at them. Each round of the game gets more and more deep, each with it's own deeply thought out games. Those who love deep story lines like Death Note will love it, especially considering the art style is similar at some points.
Currently I'm on chapter 60.