“A prohibitive mode of exit,” Piercy observed with a smile.

“Yes,” Morriston said.  “I can’t understand it at all.  Besides, who would be likely to want to play tricks here?  We have had no sign of burglars, and in any case they would hardly have been able to bring a ladder long enough to reach up to that window.  Well, we must have the mystery cleared up.  I think, Stent, you had better send one of the men on a bicycle into Branchester to fetch a locksmith and have the door opened somehow.  Have it explained to him that it may be a tough job.  In the meantime we may as well go and view the tower from the outside, as we can’t get in.”

Accordingly the whole party went down into the hall and so out to the garden, where they strolled round the house, Piercy meanwhile taking notes of its architectural features.  As they came to the tower the rays of a late winter sun were striking it almost horizontally, lighting it up in a picturesque glow.  Piercy, with his archaeological knowledge, was able to tell the owner and Gifford a good deal about the ancient structure of which they had previously been ignorant.

“The sunset would have been worth seeing from that top window,” Morriston said, evidently perplexed and annoyed over the mystery of the locked door.  “I can’t make out what has happened.”

“The person who locked the door assuredly did not make his exit by the window,” Kelson remarked with a laugh, as he looked up at the sheer surface of the upper wall; “unless he was bent on suicide, in which case we should have found what was left of him at the foot of the tower.”

As they went on round the house, Miss Morriston was seen coming up the drive.  Her brother hurried forward to meet her.

“I say, Edith,” he exclaimed, “we are in a great fix.  Can you explain how the door of the top room in the tower comes to be locked with the key inside?”

Miss Morriston looked surprised.  “What, Dick?”

“We can’t get in,” Morriston explained.  “We found the door locked and the key missing, and then when Alfred tried another key, he found the right one was in the lock but inside the room.”

Miss Morriston thought a moment.  “My dear Dick, the door can’t be locked.”

“It is, I tell you,” he returned; “most certainly locked.  We have tried it and found it quite fast.”

“Then there must be someone in the room,” his sister said.

“That,” Morriston replied, “seems the only possible explanation.  But I shouted several times and got no answer.”

“Someone playing you a trick,” and the girl laughed.

“But who? who?” he returned.

His sister gave a shrug.  “Oh, you’ll find out soon enough,” she replied, with a smile.

“I shall,” he replied, as two men appeared making for the servants’ entrance.  “Here comes Henry with the locksmith.”

Miss Morriston in her stately way looked amused.