Half-way along the wall was a low, arched door. Louise d'Ernemont stopped in front of this door and opened it with a key which seemed to us enormous. Mother and child entered and closed the door. "In any case," said Lupin, "she has nothing to conceal, for she has not looked round once...." He had hardly finished his sentence when we heard the sound of footsteps behind us. It was two old beggars, a man and a woman, tattered, dirty, squalid, covered in rags. They passed us without paying the least attention to our presence. The man took from his wallet a key similar to my neighbour's and put it into the lock. The door closed behind them. And, suddenly, at the top of the lane, came the noise of a motor-car stopping.... Lupin dragged me fifty yards lower down, to a corner in which we were able to hide. And we saw coming down the lane, carrying a little dog under her arm, a young and very much over-dressed woman, wearing a quantity of jewellery, a young woman whose eyes were too dark, her lips too red, her hair too fair. In front of the door, the same performance, with the same key.... The lady and the dog disappeared from view. "This promises to be most amusing," said Lupin, chuckling. "What earthly connection can there be between those different people?" There hove in sight successively two elderly ladies, lean and rather poverty-stricken in appearance, very much alike, evidently sisters; a footman in livery; an infantry corporal; a fat gentleman in a soiled and patched jacket-suit; and, lastly, a workman's family, father, mother, and four children, all six of them pale and sickly, looking like people who never eat their fill. And each of the newcomers carried a basket or string-bag filled with provisions. "It's a picnic!" I cried. "It grows more and more surprising," said Lupin, "and I sha'n't be satisfied till I know what is happening behind that wall." To climb it was out of the question. We also saw that it finished, at the lower as well as at the upper end, at a house none of whose windows overlooked the enclosure which the wall contained. During the next hour, no one else came along. We vainly cast about for a stratagem; and Lupin, whose fertile brain had exhausted every possible expedient, was about to go in search of a ladder, when, suddenly, the little door opened and one of the workman's children came out. The boy ran up the lane to the Rue Raynouard. A few minutes later he returned, carrying two bottles of water, which he set down on the pavement to take the big key from his pocket. By that time Lupin had left me and was strolling slowly along the wall. When the child, after entering the enclosure, pushed back the door Lupin sprang forward and stuck the point of his knife into the staple of the lock. The bolt failed to catch; and it became an easy matter to push the door ajar. "That's done the trick!" said Lupin.