"I don't know yet how they killed him, but it's clear enough how they disposed of the body. That man learned in some way that it was in your cab. That is why he hired you to take him across the river. The other two men were on board the ferry too. But I paid no attention to them because I was watching him, the man in your cab. When you and he left the cab I followed you up forward. Then the other two went to the cab, of course; searched the body, and then cast it over the rail. You see now why he made you drive on last." "Of course!" "Planned with devilish cleverness!" she cried. "That is like him! Why weren't my eyes opened to his true character earlier! But I'll make him pay! If the body is missing, will it be possible to bring the crime home to the murderer?" "Difficult," said Greg. "It may be found floating in the river." "How could one find out if it was found?" "It would be taken to the morgue." "Watch for it for me, will you?" she cried eagerly. "I couldn't go to such a place. You watch for it, and if it is brought there secure it for me!" Greg promised. "What do you suppose is his object now in masquerading as the man he killed?" he asked. "That I can't guess. I know what happened; I don't know what underlies it all. We've got to find out." Once more that "we" inspired Greg to high deeds. In speaking of the man they had followed it was natural to turn to the spot where they had last seen him. As he did so Greg saw his very figure reappear once more in the lobby of the little hotel. He called the girl's attention to it. "Quick! Crank your engine!" she said excitedly. "I thought he would be coming out again!" The tall man spoke to the clerk, and the latter took down the telephone receiver. "Calling for a taxi," suggested Greg. Meanwhile he got his engine started, and climbed into the seat beside her. "Better move down the street a little way," she suggested. "He might catch sight of us here." Greg obeyed. They waited in the next block. In due course a taxi-cab drew up before the little hotel, and the tall man got in, without baggage. The cab turned west in the side street. Greg followed at a furlong's distance. This time the chase was not very long. They were led around the lower side of Union Square and down University Place. The first cab turned west in Ninth Street, and crossing Fifth Avenue drew up before a residence on the south side of the dignified, old-fashioned block beyond. Greg kept on to Sixth Avenue. "Did you get the number?" she asked. "Five-thirty." "I thought so. That's the headquarters of the politicians. I have seen him address letters there." Meanwhile the other cab having dropped its passenger had returned eastward. "Go back to that house!" ordered the girl. Her eyes were shining like embers. A great excitement possessed her. They drew up before the door of five-thirty. "Are you a brave man?" she asked abruptly.