Rating: High Five!
Who I'd Recommend to: Fans of The Blackthorn Key, Percy Jackson and the Olympians, and Peter and the Starcatchers.
Synopsis (partly from Amazon):
After the death of his dad, Martin and his mum move into an enormous stately home where they encounter a mysterious being called the Keeper of Portals, who claims to control every portal on the planet, except for the door at the end of Martin's bedroom, which has been sealed for 400 years. One morning, Martin wakes to discover the Keeper of Portals is missing and the door at the end of his bedroom has been opened. Martin steps through the door to find himself in the 17th century where he meets Isabel, the house's maid. Martin and Isabel quickly learn that everything on earth, from time and causality, to pleasantries and buttons, is controlled by its own keeper, but they soon become entangled in a battle against the Keeper of Questions. Their adventures takes them on a journey through time, ending up in London. But when they arrive there they find the town deserted - the Keeper of Questions has control of everyone in London and it won't be long until Martin and Isabel are next.