Enid Blyton 
The Mystery of the Disappearing Cat [EPUB ebook] 

Bets was feeling very excited. Her big brother Pip was coming home from school that day for the long summer holidays. She had been without him for three months, and had felt very lonely. Now she would have him again.
“And Larry and Daisy will be home tomorrow!” she said to her mother. “Oh, Mummy! it will be fun to have so many children to play with again.”
Larry and Daisy were Pip’s friends. They were older than Bets, but they let her play with them. In the Easter holidays the four of them, with another boy and his dog, had had a great adventure finding out who had burnt down a cottage.
“We were the Five Find-Outers, ” said Bets, remembering everything. “We found out the whole mystery, Mummy, didn’t we? Oh, I do wish we could solve another mystery these holidays too!”
Her mother laughed. “Oh, it was just a bit of luck that you solved the mystery of the burnt cottage, ” she said. “There won’t be any more mysteries, so don’t expect any, Bets. Now hurry up and get ready. It’s time to meet Pip.”