“What did you say?” she murmured drowsily.
“Wake up, sleepy head,” Madge said, shaking her again. “I’ve had another inspiration about the formula.”
At the word “formula” which was magic to her ears, Anne sat upright, ready to listen.
“We’ve been hopeless duds trying to bring out the secret writing by heating the pages of the book!” Madge declared.
“And you awakened me to tell me that? Of all the—”
“I’m not through. Remember, you said your Father knew a great deal about secret inks and the like.”
“He was a government specialist,” Anne corrected; “He probably knew as much about secret inks as any man in Washington.”
Madge nodded eagerly.
“Exactly. And here we’ve been working on the theory that he would use the most simple means of hidden writing. Why, you can write with milk and bring it out by heating the paper. Any school child knows that.”
“Father always had an aversion to the obvious thing too,” Anne declared, catching her friend’s trend of thought. “He probably used the very latest method of secret writing.”