The Ogre Downstairs by Diana Wynne Jones

it’s not fair.”
    “Your ages add up to more than ours,” said Malcolm.
    Caspar felt more tired than ever. “Oh, let him go, Johnny,” he said. “This is boring.”
    Johnny moved reluctantly aside. Malcolm swiftly got his hand to the doorknob. Then he said, “I don’t see I’ve any call to tell you anything. I bet you only discovered the flying powder by mistake and spilt it on Gwinny by accident.”
    The mortifying thing was that this was quite true. As Malcolm slipped round the door, Johnny said angrily, “You wait. I’ll discover something you’ve never dreamt of. You needn’t think you’re so clever.” Malcolm shut the door in his face with a bang. Johnny turned round and ploughed feverishly through the construction kits to the chemistry set. He threw himself down beside it and began to scrabble among the comics and toffee bars around it. “The instructions,” he said. “Have you seen the instructions, Caspar?”
    “No. Why?” said Caspar, yawning.
    “I’ve got to find out which tubes were on the bottom layer,” Johnny said desperately. “I’ve got them all mixed up.”
    Caspar saw reason in this. They searched fiercely. Johnny found the broken test tube that had held the flying mixture and cut his finger on it. Caspar found nothing but toffee bars and comics, until he thought to lift up the lid of the chemistry set. The outside of it said Magicator Chemistry by Magicraft. Guaranteed non-toxic, non-explosive . The inside of the lid said the same, but underneath that were instructions of a sort. Caspar read, 1. Try this experiment with Marble Chips . “These are no good,” he said. “I did all these at school.”
    “No, you fool!” said Johnny, sucking his bleeding finger. “Under your knee.”
    Caspar seized the little pamphlet he was kneeling on. Magicator Chemistry , it said. But it turned out to be a set of quite ordinary experiments, all of which either he or Johnny had done at school. And nowhere did it give a list of the substances in the set. “This is no good either,” he said, smothering a yawn.
    “All right,” Johnny said grimly. “I’ll just have to go through and test each one. I’m not going to be beaten by that stuck up toff, so there!”
    By supper time, he had sorted out the chemicals he knew, but by then he was too tired to go on. He was only too glad to trudge downstairs and sit round the table with four other people as tired as he was.
    “Good gracious!” said Sally, looking round their white faces and reddened eyes. She knew there was every reason why Douglas should be heavy-eyed and morose, but she could not understand the rest of them. “I hope you’re not all sickening for something.”
    “Only sickening in the other sense,” said the Ogre,with his usual uncanny instinct for wrongdoing. “They were fooling about half the night, that was all.”
    “Oh no, Father, I think I really am going down with something,” Malcolm said coolly. “I have a heavy feeling in my head.”
    “Serve you right,” said the Ogre.
    “And I think there must be something wrong with me too,” Gwinny said hastily. “Because I’m so quiet.”
    “Please don’t apologise,” said the Ogre politely. “It’s a welcome change.”
    The meal finished in silence both weary and nervous. Though the Ogre said nothing more, Caspar could not help keeping an anxious eye on Douglas. He was even more nervous of him than of the Ogre. When he found Douglas morosely waiting in the hall after supper, it took him some courage not to run away. But all Douglas did was to thrust the Indigo Rubber records at him.
    “They’re clean now,” he said. “Mind you keep them that way.” Then he went away upstairs. Caspar, hardly able to believe his good fortune, stood clutching the records and looking after him uncertainly. Douglas leant down over the bannisters. “I haven’t forgotten I owe you,” he said. “If I could keep my eyes open I’d give it you now.”
    It was surprising how ready