Jan Mark's "Useful Idiots" is a reasonably complex book, but absolutely brilliant for this theme. Betrayal on practically every level you could think of.

The Spy Who Came in from the Cold" is also good, and would 
probably appeal to boys.

Tamar by Mal Peet

I am not scared by Niccolo Ammaniti Now released as a movie. An authentic portrayal of childhood and an enthralling story about friendship and betrayal, guilt and innocence.

The kite runner by Khaled Hosseini The Kite Runner is a novel about friendship, betrayal, and the price of loyalty. It is about the bonds between fathers and sons, and the power of fathers over sons - their love, their sacrifices, and their lies.

Burn my heart by Beverley Naidoo

The blood of flowers by Anita Amirrezvani

My name was Judas by C.K. Stead

The Constant Gardener (Film and book.)

King Lear - play, film, book

Atonement - film, book

Clockwork Orange - film, book