"Èbrecourt branch-line," said Paul, laughing. "Seven miles in the shade. And that is how the stronghold of Corvigny was bagged. First, a few thousand men passed through, who killed off the little Ornequin garrison and the posts on the frontier and then went on to the town. At the same time, the two huge guns were brought up, mounted and trained upon sites located beforehand. When these had done their business, they were removed and the holes stopped up. All this didn't take two hours." "But to achieve those two decisive hours the Kaiser worked for seventeen years, bless him!" said Bernard. "Well, let's make a start." "Would you like my men to go with you?" suggested the lieutenant. "No, thank you. It's better that my brother-in-law and I should go by ourselves. If we find, however, that the enemy has destroyed his tunnel, we will come back and ask for help. But it will astonish me if he has. Apart from the fact that he has taken every precaution lest the existence of the tunnel should be discovered, he is likely to have kept it intact in case he himself might want to use it again." And so, at three o'clock in the afternoon, the two brothers-in-law started on their walk down the imperial tunnel, as Bernard called it. They were well armed, supplied with provisions and ammunition and resolved to pursue the adventure to the end. In a few minutes, that is to say, two hundred yards farther on, the light of their pocket-lantern showed them the steps of a staircase on their right. "First turning," remarked Paul. "I take it there must be at least three of them." "Where does the staircase lead to?" "To the château, obviously. And, if you want to know to what part, I say, to the room with the portrait. There's no doubt that this is the way by which Major Hermann entered the château on the evening of the day when we attacked it. He had his accomplice Karl with him. Seeing our names written on the wall, they stabbed the two men sleeping in the room, Private Gériflour and his comrade." Bernard d'Andeville stopped short: "Look here, Paul, you've been bewildering me all day. You're acting with the most extraordinary insight, going straight to the right place at which to dig, describing all that happened as if you had been there, knowing everything and foreseeing everything. I never suspected you of that particular gift. Have you been studying Sherlock Holmes?"