“You recognize him, do you not?” smiled Ashton-Kirk.

“I do, now,” returned Pendleton.  “It’s our friend Dr. Mercer.”

When the buggy arrived at the spot where the motor-car stood, the doctor regarded its occupants with some surprise.

“Good-morning,” greeted Ashton-Kirk.

Painfully, gaspingly the other answered this in kind.  The round white face wore an expression of martyrdom.

“I am pleased to see you once more,” said he.

“You like driving in the morning, then?” said the investigator.

The principal’s flesh quivered with repulsion.

“It is an exercise ordered by my physician,” he answered.  “I protested against it strongly, but he was obdurate.  And I am compelled to do it before I have had my breakfast,” hollowly.  “It is scarcely short of barbarous.”

Here the small horse stretched its neck and shook itself until the harness rattled.  Pendleton looking from master to beast thought they might exchange places much to the master’s ultimate well-being.

There was a short pause; then Dr. Mercer bent his head toward them.

“When you visited the institute a few nights ago,” said he, “you also, at my request, visited Professor Locke.”

Ashton-Kirk nodded.

“For some time,” proceeded the other, “I have fancied that there was something wrong with him.  Not of a physical nature, as is, unfortunately the case with myself, but more in a mental way.  But since that night I have been sure that some sort of a derangement had fixed itself upon him, or is in progress.  He can scarcely be called the same person.  More than once I have been afraid,” and here the speaker lowered his voice to a husky whisper, “that he is unbalanced.”

“That is very grave,” said Ashton-Kirk.

“It has occurred to me,” went on the doctor, not without shrewdness, “that something happened that night which unsettled him.”  The eyes seemingly floating in fat, turned themselves first to Pendleton, then to Ashton-Kirk.  “I suppose, though, you know nothing of it?”

“We noticed that he seemed greatly agitated,” replied the investigator.  “And we are alarmed to hear that he seems disturbed.”

“It is our rule that no one leave the institute grounds after nightfall,” said Dr. Mercer, in a troubled voice.  “Last night I had occasion to send for him, but he was gone.  This morning I stopped to reproach him for his absence; but apparently he has not returned.”

“You’re mistaken there,” put in Burgess.  “Look!”

He indicated the house as he spoke.  The small figure of Locke was seen emerging at the front door; he paused for a moment, peering this way and that in his near-sighted fashion, then hastily made his way toward the work-shop.  Evidently he had not seen them.

With great labor and much catching of breath Dr. Mercer had turned sufficiently to see these things.  He seemed greatly astonished.