Enid Blyton 
The Mystery of the Spiteful Letters [EPUB ebook] 

Bets and Pip were waiting impatiently for Larry, Daisy and Fatty to come. Bets was on the window-seat of the playroom looking anxiously out of the window.
“I wish they’d buck up, ” she said. “After all, they came home from boarding-school yesterday, and they’ve had plenty of time to come along. I do want to know if Fatty’s got any more disguises and things.”
“I suppose you think there’ll be another first-class mystery for us to solve these hols, ” said Pip. “Golly, that was a wizard one we had in the Christmas hols, wasn’t it?”
“Yes, ” said Bets. “A bit too wizard. I wouldn’t really mind not having a mystery these hols.”
“Bets! And I thought you were such a keen detective!” said Pip. “Don’t you want to be a Find-Outer any more?”