should be found with the body,
going to do anything so foolhardy as that?"

"He needn't have been afraid of me," said Cayley.

"Then why didn't he call for you? He knew you were about. You could
have advised him; Heaven knows he wanted advice. But the whole theory
of Mark's escape is that he was afraid of you and of everybody else,
and that he had no other idea but to get out of the room himself, and
prevent you or the servants from coming into it. If the key had been on
the inside, he would probably have locked the door. If it were on the
outside, he almost certainly wouldn't."

"Yes, I expect you're right," said Bill thoughtfully. "Unless he took
the key in with him, and locked the door at once."

"Exactly. But in that case you have to build up a new theory entirely."

"You mean that it makes it seem more deliberate?"

"Yes; that, certainly. But it also seems to make Mark out an absolute
idiot. Just suppose for a moment that, for urgent reasons which neither
of you know anything about, he had wished to get rid of his brother.
Would he have done it like that? Just killed him and then run away? Why,
that's practically suicide--suicide whilst of unsound mind. No. If you
really wanted to remove an undesirable brother, you would do it a little
bit more cleverly than that. You'd begin by treating him as a friend, so
as to avoid suspicion, and when you did kill him at last, you would try
to make it look like an accident, or suicide, or the work of some other
man. Wouldn't you?"

"You mean you'd give yourself a bit of a run for your money?"

"Yes, that's what I mean. If you were going to do it deliberately, that
is to say and lock yourself in before you began."

Cayley had been silent, apparently thinking over this new idea. With his
eyes still on the ground, he said now: "I hold to my opinion that it was
purely accidental, and that Mark lost his head and ran away."

"But what about the key?" asked Bill.

"We don't know yet that the keys were outside. I don't at all agree with
Mr. Gillingham that the keys of the down-stairs rooms are always outside
the doors. Sometimes they are, no doubt; but I think we shall probably
find that these are inside."

"Oh, well, of course, if they are inside, then your original theory
is probably the correct one. Having often seen them outside, I just
wondered that's all. You asked me to be quite frank, you know, and tell
you what I thought. But no doubt you're right, and we shall f