Stepping to a part of the wall which bore traces of crumbling away, Gracie pushed a brick into the cellar of the adjoining house; she pushed another, and that fell; another, and that fell. A rat scampered past, and gave Dick a shock. Gracie laughed. Then she wedged her small body through, and stood apart from him, he being in one house, and she in another.
"Wait a bit, Gracie," he cried excitedly. "Hold the candle."
There were other loose bricks which yielded to his pressure, and in a few moments he had made a hole large enough for a man to creep through. Dick and Gracie were now side by side.
"Easy, ain't it, Dick? We'd best put up the bricks, in case of accidents."
"You ought to have been a detective," said Dick.
"I shouldn't have made a bad one, I don't think," she answered, with unemotional complacency, proceeding to replace the bricks, which she did very carefully, even fixing the loose mortar about them. The work was done so neatly that nothing but the closest scrutiny would have led to the discovery of the unlawful communication between the houses.
"Dick," said Gracie, "Mr. Samuel Boyd was as artful as they make 'em. Do you think he went in and out through this hole?"
"He'd have been in a rare mess if he did," replied Dick, brushing the dust from his clothes. "The puzzle is what he wanted in an empty house. Supposing he did not wish to go back, how did he get out of it?"
"This way."
He followed her out of the cellar up a short, narrow flight of rickety stairs. At the end of the passage was a door, the lock of which was broken. This door opened upon half a dozen stone steps, and at one time had probably been used as a kitchen entrance for tradesmen. A little rusty gate at the top opened into the Square. Only two of the houses had an entrance of a similar description, and Dick inwardly railed at his own lack of foresight in overlooking this means of getting into Samuel Boyd's residence. Upon further reflection, however, he thought it hardly likely that he would have succeeded in carrying his investigations to the point which Gracie's shrewdness and pertinacity had enabled her to reach.