The ending is incredibly cliché and he struggles to create the tension he's achieved in his other novels like _Raven's Gate_ . Furthermore, he adds new ideas about the characters at the end that should've been introduced nearer the beginning. For example, the fact that, unlike James Bond, Alex didn't choose to be a secret agent. This should have been one of his first thoughts when he was confronted by Alan Blunt in Royal and General.
Also Anthony Horowitz needs to learn that a Physalia Physalis (otherwise known as the Portuguese Man o' War or just Man of War) is not actually a jellyfish but a sophonophore, a colonial organism made up of specialized animals of the same species - zooids or polyps.
Further more, the pace is too fast, and it skins over important parts of the main storyline, for instance when Alex's training summed up in one chapter, but somehow that gives him enough experience. Most fourteen year old boys wouldn't karate chop and defeat a trained body guard so easily.
I'm afraid to say that the characters have no depth and are increasingly cliché. For example, Nadia Vole and Herod Sayle are both foreigners, which is a common stereotype from the James Bond movies. Furthermore, we have no idea where Vole, Grin and Sayle are from or who they are except downright evil. They have no moral or physical weeknesses apart from the basic human limits. The plot would have had a nice twist if one of them helped or aided Alex, or if they betrayed Sayle in some way.