"First," he went on, "let me tell you of the arrangement of the Professor's house. The whole of the ground and first floors are devoted to reception rooms. The remaining two floors and attics are bedrooms. Now, on the first floor, reached by passing through what is known as the Red Room, a small boudoir at the back, and then through a short passage, one comes to a large and spacious studio, an addition made by a former owner, a well-known artist. The only entrance is through the Red Room. The Professor rented the house on account of this studio, and had it fitted up as a laboratory. Here, secure from intrusion, he frequently carried on his experiments, making those remarkable discoveries which have rendered him world-famous. The laboratory is shut off from the boudoir by this short passage, there being two doors, one in the boudoir itself and one at the entrance to the Professor's workshop. To both these doors are patent locks, of which the Professor keeps the keys, carrying them upon his watch-chain. No one else has a key, while the door from the conservatory over the porch is walled up. This is in order that no prying person shall enter in his absence and discover what experiments are in progress--a very natural precaution." "Then they were secret experiments he was making?" I remarked. "Yes. And now for the mysterious sequence of facts. They are as follows: Next morning, when the servants opened the house, one of the maids found, lying upon the hall table, a note addressed to Miss Greer. When Ethelwynn opened it, she found it to be from her father, telling her with regret that he must be absent abroad for several months, but that she was not to feel uncomfortable, and giving her certain directions, as well as how to obtain money during his enforced absence." "Well?" Joseph, the parrot, set up a loud screeching, trying to attract his master's attention.