The result was the next morning they decided that they really would go and tell the whole thing to the Professor. “He’ll write to Father if he thinks there is really something wrong with Lu，” said Peter； “it‘s getting beyond us.” So they went and knocked at the study door， and the Professor said “Come in，” and got up and found chairs for them and said he was quite at their disposal. Then he sat listening tothem with the tips of his fingers pressed together and never interrupting， till they had finished the whole story. After that he said nothing for quite a long time. Then he cleared his throat and said the last thing either of them expected：
“How do you know，” he asked， “that your sister’s story is not true？”
“Oh， but.” began Susan， and then stopped. Anyone could see from the old man‘s face that he was perfectly serious. Then Susan pulled herself together and said， “But Edmund said they had only been pretending.”