“What?  Arrest him!” cried Innes.

“Precisely.  But I rather fancy,” added the inspector, grimly, “that Mr. Stokes will think twice before taking leaps like that in the dark again.”

“You say he tried to arrest him.  What do you mean by that?”

“I mean that Nicol Brinn, leaving Stokes locked in his chambers, went out and has completely disappeared!”

“But the woman?”

“Ah, the woman!  There’s the rub.  If he had lain low and followed the woman, all might have been well.  But who she was, where she came from, and where she has gone, we have no idea.”

“Nicol Brinn must have been desperate to adopt such measures?”

Detective Inspector Wessex nodded.

“I quite agree with you.”

“He evidently had an appointment of such urgency that he could permit nothing to stand in his way.”

“He is a very clever man, Mr. Innes.  He removed the telephone from the room in which he had locked Stokes, so that my blundering assistant was detained for nearly fifteen minutes—­detained, in fact, until his cries from the window attracted the attention of a passing constable!”

“Nicol Brinn’s man did not release him?”

“No, he said he had no key.”

“What happened?”

“Stokes wanted to detain the servant, whose name is Hoskins, but I simply wouldn’t hear of it.  I am a poor man, but I would cheerfully give fifty pounds to know where Nicol Brinn is at this moment.”

Innes stood up restlessly and began to drum his fingers upon the table edge.  Presently he looked up, and: 

“There’s a shadow of hope,” he said.  “Rector—­you know Rector?—­had been detailed by the chief to cover the activities of Nicol Brinn.  He has not reported to me so far to-night.”

“You mean that he may be following him?” cried Wessex.

“It is quite possible—­following either Nicol Brinn or the woman.”

“My God, I hope you’re right!—­even though it makes the Criminal Investigation Department look a bit silly.”

“Then,” continued Innes, “there is something else which you should know.  I heard to-day from a garage, with which Mr. Harley does business, that he hired a racing car last night.  He has often used it before.  It met him half-way along Pall Mall at seven o’clock, and he drove away in it in the direction of Trafalgar Square.”

“Alone?”

“Yes, unfortunately.”

“Toward Trafalgar Square,” murmured Wessex.

“Ah,” said Innes, shaking his head, “that clue is of no importance.  Under the circumstances the chief would be much more likely to head away from his objective than toward it.”

“Quite,” murmured Wessex.  “I agree with you.  But what’s this?”

The telephone bell was ringing, and as Innes eagerly took up the receiver: 

“Yes, yes, Mr. Innes speaking,” he said, quickly.  “Is that you, Rector?”

The voice of Rector, one of Paul Harley’s assistants, answered him over the wire: