Stranger by Harlan Coben

Adam Price has a lot to lose: a comfortable marriage to a beautiful woman, two wonderful sons, and all the trappings of the American Dream - a big house, a good job, a perferct life.

But then he meets a stranger ina bar.  And he learns a devastating secret about his wife.

With the mirage of perfection shattered, Adam finds himself caught up in something far darker than he realised.  And if he doesn't make the right moves, the conspiracy he's stumbled into will not only ruin lives, it will end them.