The Mysterious Benedict Society Series by Trenton Lee Stewart
Four very special children are challenged to go on a secret mission that only the most intelligent and resourceful children could complete. To accomplish it they will have to go undercover at the Learning Institute for the Very Enlightened, where the only rule is that there are no rules. As our heroes face physical and mental trials beyond their wildest imaginations, they have no choice but to turn to each other for support. But with their newfound friendship at stake, will they be able to pass the most important test of all?
(Note: allow 3-5 days for delivery)