"It was obviously Milburgh," said Whiteside. "He comes to you in the night--we know that he is in Hertford. We know, too, that he tried to assassinate you because he thought the girl had betrayed him and you had unearthed his secret. He must have killed his wife, who probably knows much more about the murder than the daughter." Tarling looked at his watch. "Ling Chu should be here by now," he said. "Oh, you sent for Ling Chu, did you?" said Whiteside in surprise. "I thought that you'd given up that idea." "I 'phoned again a couple of hours ago," said Tarling. "H'm!" said Whiteside. "Do you think that he knows anything about this?" Tarling shook his head. "I believe the story he told me. Of course, when I made the report to Scotland Yard I did not expect that you people would be as credulous as I am, but I know the man. He has never lied to me." "Murder is a pretty serious business," said Whiteside. "If a man didn't lie to save his neck, he wouldn't lie at all." There was the sound of a motor below, and Tarling walked to the window. "Here is Ling Chu," he said, and a few minutes later the Chinaman came noiselessly into the room. Tarling greeted him with a curt nod, and without any preliminary told the story of the crime. He spoke in English--he had not employed Chinese since he discovered that Ling Chu understood English quite as well as he understood Cantonese, and Whiteside was able from time to time to interject a word, or correct some little slip on Tarling's part. The Chinaman listened without comment and when Tarling had finished he made one of his queer jerky bows and went out of the room. "Here are the letters," said Whiteside, after the man had gone. Two neat piles of letters were arranged on Mrs. Rider's desk, and Tarling drew up a chair. "This is the lot?" he said. "Yes," said Whiteside. "I've been searching the house since eight o'clock and I can find no others. Those on the right are all from Milburgh. You'll find they're simply signed with an initial--a characteristic of his--but they bear his town address." "You've looked through them?" asked Tarling "Read 'em all," replied the other. "There's nothing at all incriminating in any of them. They're what I would call bread and butter letters, dealing with little investments which Milburgh has made in his wife's name--or rather, in the name of Mrs. Rider. It's easy to see from these how deeply the poor woman was involved without her knowing that she was mixing herself up in a great conspiracy." Tarling assented. One by one he took the letters from their envelopes, read them and replaced them. He was half-way through the pile when he stopped and carried a letter to the window. "Listen to this," he said: "Forgive the smudge, but I am in an awful hurry, and I have got my fingers inky through the overturning of an ink bottle." "Nothing startling in that," said Whiteside with a smile.