But perhaps it had not been such a cold-blooded killing, after all.  Suppose Cayley had had a quarrel with his cousin that afternoon over the girl whom they were both wooing.  Suppose Cayley had killed Mark, either purposely, in sudden passion, or accidentally, meaning only to knock him down.  Suppose that this had happened in the passage, say about two o’clock, either because Cayley had deliberately led him there, or because Mark had casually suggested a visit to it. (One could imagine Mark continually gloating over that secret passage.) Suppose Cayley there, with the body at his feet, feeling already the rope round his neck; his mind darting this way and that in frantic search for a way of escape; and suppose that suddenly and irrelevantly he remembers that Robert is coming to the house at three o’clock that afternoon—­automatically he looks at his watch—­in half an hour’s time ....  In half an hour’s time.  He must think of something quickly, quickly.  Shall he bury the body in the passage and let it be thought that Mark ran away, frightened at the mere thought of his brother’s arrival?  But there was the evidence of the breakfast table.  Mark had seemed annoyed at this resurrection of the black sheep, but certainly not frightened.  No; that was much too thin a story.  But suppose Mark had actually seen his brother and had a quarrel with him; suppose it could be made to look as if Robert had killed Mark—­

Antony pictured to himself Cayley in the passage, standing over the dead body of his cousin, and working it out.  How could Robert be made to seem the murderer, if Robert were alive to deny it?  But suppose Robert were dead, too?

He looks at his watch again. (Only twenty-five minutes now.) Suppose Robert were dead, too?  Robert dead in the office, and Mark dead in the passage how does that help?  Madness!  But if the bodies were brought together somehow and Robert’s death looked like suicide? ....  Was it possible?

Madness again.  Too difficult. (Only twenty minutes now.) Too difficult to arrange in twenty minutes.  Can’t arrange a suicide.  Too difficult ....  Only nineteen minutes ....

And then the sudden inspiration!  Robert dead in the office, Mark’s body hidden in the passage—­impossible to make Robert seem the murderer, but how easy to make Mark!  Robert dead and Mark missing; why, it jumped to the eye at once.  Mark had killed Robert—­accidentally; yes, that would be more likely—­and then had run away.  Sudden panic .... (He looks at his watch again.  Fifteen minutes, but plenty of time now.  The thing arranges itself.)

Was that the solution, Antony wondered.  It seemed to fit in with the facts as they knew them; but then, so did that other theory which he had suggested to Bill in the morning.

“Which one?” said Bill.

They had come back from Jallands through the park and were sitting in the copse above the pond, from which the Inspector and his fishermen had now withdrawn.  Bill had listened with open mouth to Antony’s theory, and save for an occasional “By Jove!” had listened in silence.  “Smart man, Cayley,” had been his only comment at the end.