"These five nails we hear so much about are really the key to the lock, but until the movable impediments—or, to give them their technical name, the 'tumblers'—are so arranged as to release the key, the lock cannot be opened."
"It's a rum sort of key, with no keyhole," said Kingsland.
"The key to open this lock is a mental one, rather than one of steel and iron. In other words, a puzzle lock like this always has certain movable parts, the movement of which constitutes the enigma."
"Ever heard of any locks like this one?"
"Not exactly, but the Russians, Hindoos and the Chinese have their puzzle locks in the shape of birds or animals, and they're locked or unlocked by pressing certain parts of their bodies. You can depend on it, some spring must be worked first, which relieves the nails from their tension and permits one to work the combination."
"But no such catch or spring is visible."
"Of course not. It would be the most carefully concealed of all the mechanism; but some lucky fellow will stumble on it eventually, and if he has presence of mind enough to press the nails also— Presto! your door will fly open."
"And what will he find?" asked Kent-Lauriston.
"From present appearances," replied Mr. Riddle, "a little pile of dust, which some centuries before was a letter——"
"I shouldn't be satisfied with anything less than a mouldering skeleton in chains," said Kingsland.