I think this is the only book in Anthony Horowitz's Gatekeepers quintology where I wasn't too impressed at the title.
I'm going to post a few spoilers (kind of) for the first book, Raven's Gate, so I'll put it behind a cut for the benefit of anyone who wants to read the series without finding out too much.
In the first book, it was revealed that Matt is one of five "gatekeepers", who are responsible for guarding a series of gates around the world that the "old ones" are trying to escape throgh into our world. In this book, a second gatekeeper, named Pedro, is introduced; he and Matt experience shared dreams, during which they can communicate to each other . The next book, Nightrise revolves around a new character called Jamie, who is presumably the third gatekeeper.
This book opens with Matt's aunt watching the TV, only something isn't quite right - the presenter on the quiz show she is watching is apparently talking to her (this is later shown to be some sort of mind manipulation trick by the "old ones", who featured in the first book, but it influences her to hijack an oil tanker and commit an act of terrorism - a suicide attack on Matt's school.
However, moments before the attack, Matt has a premonition, and pulls the fire alarm, evacuating the whole school, so only his aunt is killed in the attack.
The storyline then leads Matt to Peru, where the tone of the story changes somewhat, and feels more like an action/adventure story than a fantasy novel, as Matt discovers that even the police are working against him. The story also introduces a truly creepy villain, Salamanda, who is said to have had his head elongated at birth (I am not sure if this is a real practice from South America).
I was a little concerned when the plot involved Matt having his skin dyed so that he would fit in with the locals (my thought was, "Is this racist?"), but the only real faults I could find with this story was that several chapters seemed to be all about characters travelling to various places, and only just surviving attacks from their pursuers, and that Matt's telekinetic abilities seemed very under-used. At the start of the book, Matt uses his powers to get revenge on the school bully, then they aren't mentioned again until the denouement of the book.
Overall, I didn't enjoy this quite as much as the first book; I loved the mystery element and the spooky atmosphere that it posed, but the excitement factor went up a lot towards the end of the book, including Salamanda coming up with a very modern way to ensure that his plans are accomplished (it involves technology). The ending seems to take the series in a direction that I hadn't expected, and there was a plot element involving Matt walking through a door in Shoreditch and finding himself in an Italian monastery that isn't really justified until the last chapter.
I am excited to read the other three books in the series.