“Am I my brother’s keeper?” she laughed merrily.  “Come, now.  Who is this wonderful Graeme Mackenzie?  First show me that I know him.  You know the rule in a murder case—­you must prove the Corpus delicti.”

Drummond was furious.  She was so baffling.  That was his weak point and she had picked it out infallibly.  Whatever his suspicions, he had been able to prove nothing, though he suspected much in the buying and selling of Constance.

A week of bitterness, of a constant struggle against the wiles of one of the most subtle sleuths followed, avoiding hidden traps that beset her on every side.  Was this to be the end of it all?  Was Drummond’s heroic effort to entangle her to succeed at last?

She felt that a watch of the most extraordinary kind was set on her, an invisible net woven about her.  Eyes that never slept were upon her; there was no minute in her regular haunts that she was not guarded.  She knew it, though she could not see it.

It was a war of subtle wits.  Yet from the beginning Constance was the winner of every move.  She was on her mettle.  They would not, she determined, find Graeme through her.

Days passed and the detectives still had no sign of the missing man.  It seemed hopeless, but, like all good detectives, Drummond knew from experience that a clue might come to the surface when it was least expected.  Constance on her part never relaxed.

One day it was a young woman dressed in most inconspicuous style who followed close behind her, a woman shadow, one of the shrewdest in the city.

A tenant moved into the apartment across the hall from Constance, and another hired an apartment in the next house, across the court.  There was constant espionage.  She seemed to “sense” it.  The newcomer was very neighborly, explaining that her husband was a traveling salesman, and that she was alone for weeks at a time.

The lines tightened.  The next door neighbor always seemed to be around at mail time, trying to get a look at the postmarks on the Dunlap letters.  She had an excuse in the number of letters to herself.  “Orders for my husband,” she would smile.  “He gets lots of them personally here.”

All their ingenuity went for naught.  Constance was not to be caught that way.

They tried new tricks.  If it was a journey she took, some one went with her whom she had to shake off sooner or later.  There were visits of peddlers, gas men, electric light and telephone men.  They were all detectives, also, always seeking a chance to make a search that might reveal her secret.  The janitor who collected the waste paper found that it had a ready sale at a high price.  Every stratagem that Drummond’s astute mind could devise was called into play.  But nothing, not a scrap of new evidence did they find.

Yet all the time Constance was in direct communication with Mackenzie.

Graeme, in his enforced idleness, was more deeply in love with Constance now than ever.  He had eyes for nothing else.  Even his fortunes would have been disregarded, had he not felt that to do that would have been the surest way to condemn himself before her.