Evil Star by Anthony Horowitz

The first gate was closed, but there is danger of a second gate being opened. Matt and Richard must travel to Peru, where they will face ambushes, traitors, and many more dangers. The second of the five is found.

This is the second book in the Gatekeepers, and just as excellent as the first. The story progresses quickly and suspensefully. If you haven't read the first one, read it first; however, don't forget to read the entire series. You won't regret it!