He pointed at the table and Sir Walter caught his breath with a sort of curse at his own blindness.  For the candle in the candlestick had obviously burned itself away to nothing and left him, mentally, at least, very completely in the dark.

“Then there is a sort of mathematical question,” went on Fisher, leaning back in his limp way and looking up at the bare walls, as if tracing imaginary diagrams there.  “It’s not so easy for a man in the third angle to face the other two at the same moment, especially if they are at the base of an isosceles.  I am sorry if it sounds like a lecture on geometry, but—­”

“I’m afraid we have no time for it,” said Wilson, coldly.  “If this man is really coming back, I must give my orders at once.”

“I think I’ll go on with it, though,” observed Fisher, staring at the roof with insolent serenity.

“I must ask you, Mr. Fisher, to let me conduct my inquiry on my own lines,” said Wilson, firmly.  “I am the officer in charge now.”

“Yes,” remarked Horne Fisher, softly, but with an accent that somehow chilled the hearer.  “Yes.  But why?”

Sir Walter was staring, for he had never seen his rather lackadaisical young friend look like that before.  Fisher was looking at Wilson with lifted lids, and the eyes under them seemed to have shed or shifted a film, as do the eyes of an eagle.

“Why are you the officer in charge now?” he asked.  “Why can you conduct the inquiry on your own lines now?  How did it come about, I wonder, that the elder officers are not here to interfere with anything you do?”

Nobody spoke, and nobody can say how soon anyone would have collected his wits to speak when a noise came from without.  It was the heavy and hollow sound of a blow upon the door of the tower, and to their shaken spirits it sounded strangely like the hammer of doom.

The wooden door of the tower moved on its rusty hinges under the hand that struck it and Prince Michael came into the room.  Nobody had the smallest doubt about his identity.  His light clothes, though frayed with his adventures, were of fine and almost foppish cut, and he wore a pointed beard, or imperial, perhaps as a further reminiscence of Louis Napoleon; but he was a much taller and more graceful man that his prototype.  Before anyone could speak he had silenced everyone for an instant with a slight but splendid gesture of hospitality.

“Gentlemen,” he said, “this is a poor place now, but you are heartily welcome.”

Wilson was the first to recover, and he took a stride toward the newcomer.

“Michael O’Neill, I arrest you in the king’s name for the murder of Francis Morton and James Nolan.  It is my duty to warn you—­”

“No, no, Mr. Wilson,” cried Fisher, suddenly.  “You shall not commit a third murder.”

Sir Walter Carey rose from his chair, which fell over with a crash behind him.  “What does all this mean?” he called out in an authoritative manner.