SOLVED. Adult Action book about guy who finds diamonds in train station. [s]n

[Aimee]

Hello, this is my first post - thank you in advance.
Spoilers alert.

This is a book I read about 10 years ago. Set in the US.

It starts with a guy finding diamonds in a locker within a train station. He steals them and hides them.

There is another character who is ex-military and works with other ex-military people on private hire jobs. He has returned to university - I think it was to study art.

Midway through the book, one character turns to his fiance in a hotel room and you realise that both the thief and ex-military person are the same character in a fantastic plot twist.

I think one of the characters was known as The Shadow.

I was trying to explain the book to a friend and can't remember the name. I had thought it would be easy to search for, but I can't find it anywhere!

Thank you.

[Will]

Kill Me If You Can by James Patterson

[Aimee]

Thank you very much. That's the one! Much appreciated :)