A prequel with the events leading up to his rescue from the sea in the first film,got to be a good film in that,but may be copyrighted.
The first film kept vaguely to the storyline of the first book, but left a lot out. The second and third films went off at such a tangent that the fourth film could never be brought back in line with the book. The fourth book is about him competing with a younger assassin, but I don't want to spoil it for anyone ! Still, it's a good read, even if wasn't written by Ludlum ! Despite all that, the films have been really watchable in their own rights - you just need to forget about the storyline in the books !