A man (who we eventually get to know as Jason Bourne) is found unconscious at sea with bullet wounds. He is nursed back to physical health by an alcoholic washed out doctor at the local port. When he wakes he has no memory of who he is or anything from his past. The only clue is a series of numbers which are a bank account in Zurich. As he recovers he also discovers a few things about himself with the assistance of the doctor. He seems to be familiar with Asian cultures, has considerable knowledge of martial arts and weaponry, and he has had cosmetic work done to make him appear more ordinary.
From here Bourne journeys to Zurich to find the bank account and hopefully discover who he is. Along the way he makes more discoveries about himself and finds out that he is wanted by amongst others the American government. The book then follows his efforts to find out who he is, what he is being hunted for and whether he did it.
The plot is very interesting - it's a who dun it where the supposed perpetrator doesn't know if he's guilt. The challenges facing Bourne are huge, as are the decisions - if he is guilty how much does he want to find out? Is he accountable for the actions of the person he no longer is. The action rattles along at a good pace, and there are a glut of interesting and complex characters involved in the hunt for Bourne. I would very strongly recommend this for those that have seen the film as although the premise and main characters are the same the plot takes a more involving route here and the development and torment of Bourne as he learn more about his previous self is fascinating.
If you're a Ludlam fan you've probably read something very similar in setting before, as most of his books are about an agent supposedly gone rogue who needs to prove his innocence, but in my opinion Jason Bourne is his finest creation.