This series is perhaps a bit more suitable to a slightly older tween/teen than Horowitz's other series, Alex Rider. There is a lot of action and suspense as five teens realize their talents are from older beings and need to fight the encroaching evil that is threatening the world. This fourth installment in the series finds the main character, Matt, in Hong Kong, where he discovers the identity of the fifth Gatekeeper, Scar. The action is pretty much nonstop and sets us up for the next (final) story. Definitely waiting for number five!