Você pode estar procurando por The Guardians de John Christopher.
Rob is a 13-year-old orphan following the death of his father. There is considerable suspicion and secrecy surrounding his death. Rob is sent away to a State boarding school where harsh disciplinary measures and ritual bullying by seniors soon make life intolerable; in his desperation, he devises a plan of escaping to the County, reasoning that he will avoid detection there much more easily than anywhere in the heavily-surveillanced Conurbs. He is further driven by the fact that his mother was also from the County and had herself crossed over into the Conurbs to be with his father.
Slipping out and making his way to Reading, he comes up against the Barrier dividing that Conurb from the County adjacent. The Barrier, unmanned, proves be a much less of a challenge than popular rumour suggests, and, finding a spot at which he is able to dig a gap underneath that is large enough to pass through, Rob crosses over into the County. He takes in his expansive surroundings as he continues north-west but does not manage a long distance before he is noticed. A figure on horse spots him and gives chase, catching up quickly as Rob twists his foot running.
....
The next day, a patrol stops at the Gifford house with orders to escort Rob for questioning. Rob's initial apprehensions about this are calmed when he is taken not to law enforcement but to Old Hall, Sir Percy Gregory's home. Over coffee and cherry cake, Rob comfortably recounts his old Nepal backstory again in response to Sir Percy's prompting questions. Sir Percy, however, shocks him when complimenting him by using his real surname. It becomes clear that Rob's true identity has been known to him for a long time now and that the authorities have tolerated his presence in the County. Using this as leverage, Sir Percy attempts to manipulate Rob into informing. Rob tells him everything except for Mike's late-night visit and the secret address; this seems to satisfy Sir Percy, though he had been hoping to find out more about the leaders of the movement and their present location. Disturbingly, Sir Percy tells Rob of what is to be done with Mike if he is found: a certain surgical procedure on the brain which renders the subject docile and obedient. He also tells Rob of the secret group of overseers responsible for the present system (the titular "Guardians") and, having appraised the intelligence and initiative Rob has shown in coming this far, offers to recruit him.