‘That’s the first thing we must do. Go and see Gladys, and ask her if she knows or guesses who could have written her that letter. We must also find out what’s in it.’

‘Let’s go now,’ said Pip, who always liked to rush off as soon as anything had been decided.

‘Right. You take us,’ said Fatty. Pip looked rather blank.

‘But I don’t know where Gladys lives,’ he said.

‘Ha, I thought you didn’t,’ said Fatty. ‘Well, Pip, you must find out. That’s the first thing we’ve got to do - find out where Gladys lives.’

‘I could ask Mother,’ said Pip doubtfully.

‘Now don’t be such a prize idiot,’ said Fatty at once. ‘Use your brains! You know jolly well your parents don’t want us mixed up in this mystery, and we’ve got to keep it dark that we’re finding out things. Don’t on any account ask your mother anything - or Mrs. Moon either.’

‘Well, but how am I to find out then?’ said Pip, looking bewildered.

‘I know a way, I know a way!’ sang out Bets suddenly. ‘Gladys lent me a book once and I didn’t have time to give it her back before she left. l could go to Mrs. Moon and tell her, and ask her for Gladys’s address so that I could send the book on to her.’

‘Clever girl!’ said Fatty. ‘You’re coming on well, you are, Bets! Perhaps you’d better handle this, and not Pip.’