Skeleton Key question

I've been reading Skeleton Key I it's pretty good so far. Some of what has happened is that a schoolboy called Alex Rider. He gets called by M16 which is a secret agent organization that has been using Alex ever since his uncle, Ian Rider, died for missions. He is called to go to a Tennis tournament to be a ball boy as an inside agent to make sure everything stays good because of a past break in. He notices how some players do bad on their match and seem dazed. As he investigates he finds out that a guard for the Tennis park has been doing some curious actions. All the players that lost were playing the same guy and were drugged just enough to make them off balance and not play well. In the next few chapters I think I know what will happen because of the books I've already read so I don't want to give to much away. So far I would rate this book 4-4.5 starts because its just one of my favorites and only series I've ever tried reading. .