Peter, being Peter, would probably either (a) put it on his dressing-table and forget about it, only to have it discovered by his mother tidying his room after he's gone back to school, or (b) also not really thinking, put it into his school trunk, to have it discovered by the matron at a routine drawer inspection..... In neither case would he have any idea of selling it - it wouldn't occur to him - but official panic ensues.