This is one of the best action spy thrillers I saw, and believe me I've seen a lot.
Even by today's standards, it would be good, provided someone cared to restore it's brightly colour, perfect editing, and natural sound. The alternate soundless shots of a knife fight inside the hotel swimming pool, where he can see each detail of two athletic actors actually going at it, and the merry sounds of tourists on the esplanade above while still unawares of the drama close-by, has NEVER been recreated in any film, possibly because it was too much trouble, or there were no Horst Buccholz and Mario Adorf around.
The dialog was OK, and true grit, real lines, and delivered with realism. In that not only Buccholz was good, but the other actors, too, therefore grabbing the spectator into a quite realistic scenario. The story develops from a predictable ending into something quite different, therefore we miss the presence of Koscina in the later part of the story, but it is all for the best of the film.
The director was defending his name and career, but also his money in more ways than one, as he was one of the producers investing in the project through Isasi (Barcelona, Spain). It is a pity that there was never a VHS around that I know of, and that no DVD is made of such a precious B jewel.