Code XIII is a really fascinating story. Once you start a book, you can not live without reading the following one. No wonder why it's got such a success in some other contries.
Everything starts with this man without a past, who can't remember anything. The only clue about his identity is the number XIII tatooed on the back of his neck (or on top of his ear, I don't remember). Quickly, some mysterious killers are after him. Little by little, as he finds out more about his so-called identity, he realizes he is engaged in a very complex political plot.
The story is set in a modern country, which looks like the United States and you will find a lot of similarities between the fiction and the history of the last 20 years.
Van Hamme is an excellent storyteller, the characters have a real density and the suspense doesn't stop. It seems the book will never finish and it is somehow frustrating, as you want to know the end but you are never sure about the real identity of the main character.
Although I am not a great fan of the drawings (a question of taste), the design is lively and very well done.
To conclude, if you are a graphic novel person, you will enjoy that book for all its qualities, and if you're not, just try! It is a great thriller, as good as a novel (unfortunately, you have to spend all your pocket money).
One more point: Van Hamme is also the author of Thorgal (fantasy book, one of the best, set in the Vikings time) and Largo Winch.