Kill Me if You Can by James Patterson and Marshall Karp
Matthew is a struggling art student in New York. A former marine who decided to follow his true passions and study art. He has just fallen in love with his art professor. While at Grand Central station, he witnesses the murder of a Russian and finds an old medical bag chock full of diamonds! Now he and his unsuspecting girlfriend are on the run.
I always read the new Patterson's. I know they can be predictable, but I always find them entertaining. This one had a nice twist to it about halfway through.