“There it is! It’s all coming up in faint brown letters!” cried Bets, thrilled. “Look! ‘My dear Clear-Orf -’ ”
“ ‘I suppose you will think...’ ” read Pip, in delight.
“Yes, it’s visible now. Golly, that’s clever, Fatty. I would never have thought that ordinary orange juice could be used as invisible ink!”
“It’s better to know that than to know about the proper invisible ink,” said Larry. “That’s expensive, but you only want an orange for this. It’s marvellous, Fatty. Let’s all write letters.”
So they all took sheets of notepaper and wrote letters in orange-juice ink. They wrote rather cheeky letters to people they didn’t like, and squealed with joy when the iron made the writing visible and they each read what the others had written.
“Did you really mean to send old Clear-Orf a letter in invisible ink?” asked Daisy, remembering what Fatty had said. “But what’s the point if he can’t read it?”
“Just the fun of the thing,” said Fatty. “He’ll be so wild to get a letter with no writing on it, and he won’t know how to read it. We shan’t tell him either!”
Fatty wrote out his first letter to Clear-Orf again, sealed up the apparently blank sheet of paper in an envelope and printed Clear-Orf’s name on it.
“It’s rather a silly thing to do, I suppose, but it’ll puzzle old Clear-Orf,” said Fatty, blotting the envelope. “Well, now I’ve taught you to write in invisible ink. Simple, isn’t it?”
“Awfully,” agreed Pip. “But I don’t quite see what use it will be to us, Fatty.”