There came a rap at the door.

“In!” said the tall man.

The door opened silently and a manservant appeared.  He was spotlessly neat and wore his light hair cropped close to the skull.  His fresh-coloured face was quite as expressionless as that of his master; his glance possessed no meaning.  Crossing to the window, he extended a small salver upon which lay a visiting card.

“In!” repeated the tall man, looking down at the card.

His servant silently retired, and following a short interval rapped again upon the door, opened it, and standing just inside the room announced:  “Mr. Paul Harley.”

The door being quietly closed behind him, Paul Harley stood staring across the room at Nicol Brinn.  At this moment the contrast between the types was one to have fascinated a psychologist.  About Paul Harley, eagerly alert, there was something essentially British.  Nicol Brinn, without being typical, was nevertheless distinctly a product of the United States.  Yet, despite the stoic mask worn by Mr. Brinn, whose lack-lustre eyes were so unlike the bright gray eyes of his visitor, there existed, if not a physical, a certain spiritual affinity between the two; both were men of action.

Harley, after that one comprehensive glance, the photographic glance of a trained observer, stepped forward impulsively, hand outstretched.  “Mr. Brinn,” he said, “we have never met before, and it was good of you to wait in for me.  I hope my telephone message has not interfered with your plans for the evening?”

Nicol Brinn, without change of pose, no line of the impassive face altering, shot out a large, muscular hand, seized that of Paul Harley in a tremendous grip, and almost instantly put his hand behind his back again.  “Had no plans,” he replied, in a high, monotonous voice; “I was bored stiff.  Take the armchair.”

Paul Harley sat down, but in the restless manner of one who has urgent business in hand and who is impatient of delay.  Mr. Brinn stooped to a coffee table which stood upon the rug before the large open fireplace.  “I am going to offer you a cocktail,” he said.

“I shall accept your offer,” returned Harley, smiling.  “The ’N.  B. cocktail’ has a reputation which extends throughout the clubs of the world.”

Nicol Brinn, exhibiting the swift adroitness of that human dodo, the New York bartender, mixed the drinks.  Paul Harley watched him, meanwhile drumming his fingers restlessly upon the chair arm.

“Here’s success,” he said, “to my mission.”

It was an odd toast, but Mr. Brinn merely nodded and drank in silence.  Paul Harley set his glass down and glanced about the singular apartment of which he had often heard and which no man could ever tire of examining.