Arnold knew German enough to know that this meant "The word is 'Freedom,'" but why it should have been spoken in a foreign language mystified him not a little. While he was thinking about this the door opened, as if by a released spring, and he saw before him a long, narrow passage, lit by four electric arcs, and closed at the other end by a door, guarded by a sentry armed with a magazine rifle. He followed Colston down the passage, and when within a dozen feet of the sentry, he brought his rifle to the "ready," and the following strange dialogue ensued between him and Colston-- "Quien va?" "Zwei Freunde der Bruderschaft." "Por la libertad?" "Für Freiheit über alles!" "Pass, friends." The rifle grounded as the words were spoken, and the sentry stepped back to the wall of the passage. At the same moment another bell rang beyond the door, and then the door itself opened as the other had done. They passed through, and it closed instantly behind them, leaving them in total darkness. Colston caught Arnold by the arm, and drew him towards him, saying as he did so-- "What do you think of our system of passwords?" "Pretty hard to get through unless one knew them, I should think. Why the different languages?" "To make assurance doubly sure every member of the Inner Circle must be conversant with four European languages. On these the changes are rung, and even I did not know what the two languages were to be to-night before I entered the house, and if I had asked for 'Mr. Brown' instead of 'Mr. Smith,' we should never have got beyond the drawing-room. "When the footman told me in German that the word was 'Freedom,' I knew that I should have to answer the challenge of the sentry in German. I did not know that he would challenge in Spanish, and if I had not understood him, or had replied in any other language but German, he would have shot us both down without saying another word, and no one would ever have known what had become of us. You will be exempt from this condition, because you will always come with me. I am, in fact, responsible for you." "H'm, there doesn't seem much chance of any one getting through on false pretences," replied Arnold, with an irrepressible shudder. "Has any one ever tried?" "Yes, once. The two gentlemen whose disappearance made the famous 'Clapham Mystery' of about twelve months ago. They were two of the smartest detectives in the French service, and the only two men who ever guessed the true nature of this house. They are buried under the floor on which you are standing at this moment." The words were spoken with a cruel inflexible coldness, which struck Arnold like a blast of frozen air. He shivered, and was about to reply when Colston caught him by the arm again, and said hurriedly-- "H'st! We are going in. Remember what I said, and don't speak again till some one asks you to do so."