One of many books that came my way was this little gem about two warring boys. Edmond Hooper lives happily in a large house with his father then his life is disrupted when a housekeeper and her young son Charles Kingshaw move in with them.
I'm the King of the Castle by Susan Hill at Amazon
Edmond is not happy and makes it very clear to his new supposed friend Charles, that he is not happy. The result is a glorious battle of wits, a tale of childhood terror as Charles realises who is King of the Castle and who is not.
I will say no more other than to recommend it as a good read. It has been filmed in French under the title under the title 'Je suis le seigneur du château' which is a wonderful version with added gloom and somewhat overwrought feel to the story.
Alas it is no longer available on DVD but if you search around the web, you might be able to locate a copy.