The Rebel Chief by Gustave Aimard

Hidden behind the passage door, the adventurer had not lost a word of what was said. When don Melchior and don Antonio rose, don Jaime, not knowing by what door they would go out, hastily left the passage, glided into the corral, and waited in concealment behind the hedge. But, a few minutes after, as nothing had stirred, and no noise was heard, he ventured to leave his hiding place and enter the passage again.

Then he approached the door, and applied his eye to the crack through which he had been previously able to see all that went on in the room. The two men bad just gone; don Felipe was alone, still seated at the table, and drinking. The adventurer's resolution was at once formed: placing the blade of his knife between the crack against the bolt, he noiselessly opened the door, silently approached the guerillero, and revealed his presence to him in the somewhat startling way we described at the end of the preceding chapter.