“You are not in earnest, I hope, Mr. Hamel,” he said, “when you tell me that you must leave early?  I have been anticipating a long evening.  My library is filled with books on South America which I want to discuss with you.”

“Another evening, if you don’t mind,” Hamel begged.  “To-night I must ask you to excuse my hurrying away.”

Mr. Fentolin looked up from underneath his eyelids.  His glance was quick and penetrating.

“Why this haste?”

Hamel shrugged his shoulders.

“To tell you the truth,” he admitted, “I had an idea while I was reading an article on cantilever bridges this morning.  I want to work it out.”

Mr. Fentolin glanced behind him.  The door of the dining-room was closed.  The servants had disappeared.  Meekins alone, looking more like a prize fighter than ever in his somber evening clothes, had taken the place of the butler behind his master’s chair.

“We shall see,” Mr. Fentolin said quietly.

CHAPTER XXX

Mr. Fentolin pointed to the little pile of books upon the table, the deep easy-chair, the green-shaded lamps, the decanter of wine.  He had insisted upon a visit, however brief, to the library.

“It is a student’s appeal which I make to you, Mr. Hamel,” he said, with a whimsical smile.  “Here we are in my study, with the door closed, secure against interruption, a bright fire in the grate, a bowling and ever-increasing wind outside.  Let us go together over the ground of your last wonderful expedition over the Andes.  You will find that I am not altogether ignorant of your profession, or of those very interesting geological problems which you spoke of in connection with that marvellous railway scheme.  We will discuss them side by side as sybarites, hang ourselves around with cigarette smoke, drink wine, and presently coffee.  It is necessary, is it not, for many reasons, that we become better acquainted?  You realise that, I am sure, and you will not persist in returning to your selfish solitude.”

Hamel’s eyes were fixed a little longingly upon some of the volumes with which the table was covered.

“You must not think me ungrateful or churlish, Mr. Fentolin,” he begged.  “I have a habit of keeping promises which I make to myself, and to-night I have made myself a promise that I will be back at the Tower by ten o’clock.”

“You are obdurate?” Mr. Fentolin asked softly.

“I am afraid I am.”

Mr. Fentolin busied himself with the handle of his chair.

“Tell me,” he insisted, “is there any other person save yourself to whom you have given this mysterious promise?”

“No one,” Hamel replied promptly.

“I am a person very sensitive to atmosphere,” Mr. Fentolin continued slowly.  “Since the unfortunate visit of this man Dunster, I seem to have been conscious of a certain suspicion, a little cloud of suspicion under which I seem to live and move, even among the members of my own household.  My sister-in-law is nervous and hysterical; Gerald has been sullen and disobedient; Esther has avoided me.  And now—­well, I find even your attitude a little difficult to understand.  What does it mean, Mr. Hamel?”