The Client by John Grisham

Mark Sway, an eleven years old child, naughty but very intelligent, accidently gets involved in a series of bad happenings. He witnesses a suicide which further leads into a series of calamities. There are many secrets behind this suicide. FBI is trying to get to the root of it, for them Mark is the Ace; FBI is behind Mark, wanting him to solve the mystery for them. This suicide shatters the underworld too. The criminals are also behind Mark when he meets an advocate; Reggie Love. Together, Mark and Reggie start shaking the very foundation of the legal system, revealing the hideous secrets of the underworld; one by one. They intercept the very core of American society, bringing forth the tie ups between the Law and Order and the Underworld, shattering the common minds.