"That's very strange?" remarked the man. "I've let nobody in since Mr Trustram, of the Admiralty, went away--about a quarter of an hour ago." "Has he been here?" Jack asked. "I met him here the other day. He struck me as being a rather surly man, and I didn't like him at all," declared Sainsbury, with his usual frankness. "Neither do I, sir, strictly between ourselves," replied Thomasson quite frankly. "He's been here quite a lot lately. His wife consulted the master about three months ago, and that's how they first met, I believe. But can't you get in?" "No. Curious, isn't it?" "Very. The doctor never locks his door in the usual way," Thomasson said, ascending the stairs with Sainsbury, and himself trying the handle. He knocked loudly, asking-- "Are you in there, sir?" But still no response was given. "I can't make this out, Mr Sainsbury," exclaimed the man, turning to him with anxiety on his pale face. "The key's in the lock--on the inside too! He must be inside, and he's locked himself in. Why, I wonder?" Jack Sainsbury bent and put his eye to the keyhole. The room within was lit, for he could see the well-filled bookcase straight before him, and an empty chair was plainly visible. Instantly he listened, for he thought in the silence--at that moment there being an absence of traffic out in the street--that he heard a slight sound, as though of a low, metallic click. Again he listened, holding his breath. He was not mistaken. A slight but quite distinct sharp click could be heard, as though a piece of metal had struck the window-pane. Once--twice--it was repeated, afterwards a long-drawn sigh. Then he heard no more. "Open the door, Jerrold!" he cried impatiently. "Don't play the fool. What's the matter, old chap?" "Funny--very funny--isn't it!" Thomasson exclaimed, his brows knit in mystification. "Most curious," declared Sainsbury, now thoroughly anxious. "How long was Mr Trustram here?" "He dined out with the doctor--at Prince's, I think--and they came back together about half-past nine. While Mr Trustram was here he was on the telephone twice or three times. Once he was rung up by Mr Lewin Rodwell." "Mr Lewin Rodwell!" echoed Sainsbury. "Did you happen to hear anything of their conversation?" "Well, not much, sir," was the servant's discreet reply. "I answered the 'phone at first, and it was Mr Rodwell speaking. He told me who he was, and then asked if Mr Trustram was with the doctor. I said he was, and at once went and called him." "Did Mr Trustram appear to be on friendly terms with Mr Rodwell?" asked the young man eagerly. "Oh! quite. I heard Mr Trustram laughing over the 'phone, and saying `All right--yes, I quite understand. It's awfully good of you to make the suggestion. I think it excellent. I'll propose it to-morrow--yes, at the club to-morrow at four.'" Suggestion? What suggestion had Lewin Rodwell made to that official of the Transport Department--Lewin Rodwell, of all men!