Eight Days of Luke by Diana Wynne Jones

David got left behind. When he caught up with them at the door of the cafe, Luke was saying: “I quite thought you were David’s sister. You look so young.”
    Astrid beamed at him, and continued to smile while they found a table and sat down. David sat down with them, rather thoughtfully. He was not sure that Luke was behaving quite honestly. Luke knew perfectly well that Astrid was not David’s sister, because David had told him all about her yesterday. He was simply buttering Astrid up. David would have been annoyed, if he had not been pretty certain that Luke was only doing it to give David a more pleasant afternoon than he would have had otherwise.
    Whatever his motives, Luke thoroughly enjoyed himself in that cafe. So did David. And, David suspected, so did Astrid too. The odd thing about Astrid was that, when Cousin Ronald was not there to stop her, she loved spending money. She spent lavishly in that cafe. Luke’s appetite was even larger than David’s. He had five milk shakes to David’s three, and four ice creams to David’s two. Astrid ate one out of a plate of cakes, and then Luke and David finished them. David felt pleasantly full for the first time that holiday. Luke must have been nearly bursting.
    Astrid continued to smile. And, instead of telling Luke all about her aches and pains, which David very much feared she would, she joked about both their appetites. “Are you sure that number of ice creams will keep you going?” she asked. “It says Banquets Arranged here. How about it? Ten courses is a bit mingy, though, isn’t it? Luke would starve. Should I just go out and get an ice-cream factory?”
    â€œWhy not?” said Luke.
    â€œWell, it’s fitting it into the Mini,” said Astrid, and David was amazed at the difference being in a good mood made to her. He only remembered Astrid being this jolly three or four times, some years ago, when he had first come to live with his relations, and that had only been on rare occasions. Yet here she was, her face all pink with laughter, opening her handbag to take out a cigarette and taking a mock-guilty look round the cafe, as if Uncle Bernard might be there disguised as a waitress. Uncle Bernard classed cigarettes below bubble gum.
    â€œDon’t tell on me, David,” she said. “Have you got a match?”
    David felt in his pocket for his matchbox, and was about to say that Astrid must not tell on him either; but, before he could fetch the box out, Luke leaned forward and snapped his fingers at the end of Astrid’s cigarette. There was a flame like a match-flame for a split second, and then the cigarette was alight. Astrid’s eyes were wide with amazement beyond it.
    â€œHow ever did you do that?” she said through a cloud of smoke.
    â€œA trick I learned ages ago,” Luke said modestly.
    â€œI’ve never seen it done before!” said Astrid. Then, not unnaturally, she became very interested in Luke and asked who were his parents and where he lived. But Luke—to David’s disappointment, because he would have liked to know too—was not telling. “But where do you live?” Astrid said cajolingly.
    Luke smiled. “At the very tip of South America.”
    â€œOh, you!” said Astrid.
    Before Astrid could ask more, Luke began cajoling in his turn. In two minutes flat, he had persuaded Astrid to buy David comfortable clothes—a thing David knew he could not have done himself if he had talked for a month. Astrid agreed that the neat and comfortable clothes Luke was wearing would be far better for David than Aunt Dot’s kind. But she stuck on the thought of Aunt Dot.
    â€œDot’ll kill us both if we come back with those,” she said. She thought about it, while David and Luke exchanged a rather hopeless look. “I tell you what!” Astrid said suddenly. “David, can you keep a secret?”
    â€œYes,” said