The Rainhams were amongst the few friends who knew the true facts of Monkton's disappearance. And, in almost morbid sensitiveness, Sheila had withdrawn a little from them. Even sympathy hurt her at such a time.

But the sudden arrival of this photo of the young Society beauty brought old memories of friendship and affection. They had played together as children; they had told their girlish secrets to each other, and it struck her that she had been wrong, and a little unkind, in withdrawing herself from the sympathy of those who were so interested in her welfare.

Gladys, no doubt, had been hurt by this att.i.tude. She had written no note, she had not even signed the photograph. She had just sent it to recall herself to her old friend and companion. It had been sent as signal that if Sheila chose to make the smallest advance, the old relations would be at once re-established.

On the spur of the moment, she wrote a warm and impulsive note, begging Gladys to come and lunch with her that day.

"Forgive me for my long silence and absorption," she concluded. "But I know you will understand what I have lately suffered."

She sent the note round to Eaton Square by her maid, with instructions to wait for an answer. It came, and Sheila's face flushed with pleasure as she read it.

"I quite understand, and I have nothing to forgive," wrote the warm-hearted girl. "But it will be heavenly to see you again and talk together as we used."

She came round half-an-hour before lunch-time, and the pair reunited, kissed, and clung together, and cried a little, after the manner of women. Then Sheila thanked her for the present of the photo, which, she declared, did not make her look half as beautiful as she was.

Gladys looked puzzled. "But I never sent any photo to you, Sheila!

Which one is it? Let me see it."

Sheila handed it to her friend, who exclaimed, after examining it: "It is the one they took of me at the Grandcourt House Bazaar; I think it is quite a good one. But, Sheila darling, if I had sent it to you I should have written a note, at least have signed it. All this is strange--very strange! What does it mean?"

Miss Monkton coloured a little as she answered:

"Yes, I did think it strange that you did not write. I thought it so far as I am capable of thinking. But I know I have been very difficult lately, and I fancied perhaps you didn't want to make advances, and that you just sent that as a reminder of old times, trusting to me to respond."

Lady Gladys kissed her warmly. "Ah! you poor darling, I quite see," she said. "But who could have sent it? That is the puzzle."

They both discussed it, at intervals, at table, and could arrive at no solution. When Lady Gladys had left, Sheila puzzled over it all by herself, with no better result. Then, at last, weary of thinking, she telephoned to Wingate.

Austin, who was in his office, agreed that the thing was very mysterious, and that he was as much mystified as she was. He ended the brief conversation by advising her to go to Smeaton.

"Our brains are no good at this sort of thing," he said candidly. "The atmosphere of mystery seems to suit them at Scotland Yard--they breathe it every day."

She drove at once to Scotland Yard, where they knew her well by now.

Smeaton was disengaged, and she was taken to his room at once.

"Any news. Miss Monkton?" he asked eagerly. "Has that young woman called?"

The girl shook her head. "No, I waited in all day yesterday, but to no purpose. Now another strange thing has happened," and she told him briefly of the receipt of the photograph from some unknown person.

"You didn't look at the envelope, I suppose?"

"No, Mr Smeaton. I hardly ever do look at envelopes. I threw it away with the rest. It would have given you a clue, of course."

"It might," returned Smeaton, who was nothing if not cautious. He ruminated for a few moments, and then said, abruptly, "You have brought it with you?"

Sheila, who had taken that precaution, handed it to him. He turned it over, peering at it in that slow, deliberate fashion of a man who examines with the microscopic detail everything submitted to him.

"Taken, I see, by the well-known firm of Kester and Treeton in Dover Street. Well, somebody ordered it, so we've got to find out who that somebody was. I will go to them at once, and let you know the result in due course."

Sheila looked at him eagerly. She had great faith in him, although so far he had had nothing but failure to report.

"Have you formed any opinion about it?" she asked timidly.

Smeaton smiled grimly, but he answered her very kindly.

"My dear Miss Monkton, I have formed many theories about your father's disappearance, and, alas! they have all been wrong. I am leaning to distrust my own judgment. I will say no more than this. This curious incident may end as everything else has done, but I think it is worth following up. I will put you into your car, and go on to the photographers."

"Let me drive you there, and wait," urged Sheila eagerly. "I shall know the result so much quicker."

The photographers in Dover Street had palatial premises. Smeaton was ushered from one apartment to another, till he reached the private sanctum of the head of the firm, where he produced his card, and explained his errand.

Mr Kester was very obliging; he would do all he could to help, and it would only be a matter of a few moments. They kept a record of every transaction, and in all probability this was quite a recent one.

He returned very shortly. It seemed that a young lady had called a couple of days ago, and asked for half-a-dozen portraits of Lady Gladys.

On account of the Grandcourt House Bazaar, there had been a great run on the photos of the various stallholders, he explained. They happened to have a few copies of this particular picture in stock. The lady purchased six and took them away with her, saying that "they were for reproduction in the ill.u.s.trated newspapers and the usual copyright fee would be paid."

"Can you give me a description of the person who bought them?" was Smeaton's first question, when Mr Kester had concluded his story.

"My a.s.sistant who served her is a very intelligent girl. Let us have her in."

Kester 'phoned and requested Miss Jerningham to be sent to him. The fluffy-haired young lady remembered the incident perfectly, and described the dress and appearance of the young woman who had bought the photographs.

If her description was to be trusted, it was the same person who had asked to see Miss Monkton and refused to leave her name.

Smeaton, who had grown so utterly tired of theories and clues, began to believe he was on something tangible at last.

He rejoined Sheila, but he did not say much.

"I shall follow this clue," he told her. "The photo was sent for a purpose, and that woman knows why it was sent. I believe you will hear from her again, unless I scared her away."

"Mr Smeaton, do tell me what you really think. I am sure there is something curious in your mind," implored the agitated Sheila.

But the detective was not to be charmed from his reserve.

"I must think over it a lot more yet. Miss Monkton, before I can hazard any opinion," he told her in his grave, deliberate way. "If I were to reveal any half-formed idea that is running through my brain, it is one I should have to dismiss as inapplicable to the circ.u.mstances as I see them at present."

From that he would not budge. Sheila drove away with a heavy heart.

Wingate came round to dinner that night, and they talked about nothing else. The only thing they could arrive at with any certainty was that the mysterious visitor, the young woman dressed in navy blue serge costume, was the sender of the photo. But that did not help them to discover the reason she had sent it.

That night Sheila lay awake, very depressed and anxious, still puzzling over this latest mystery. Presently she dozed, and then, after a few moments of fitful sleep, woke with a start. Was it in that brief dream that some chords of memory had been suddenly stirred of a conversation held long ago between her father and a young man named Jack Wendover, a second secretary in the diplomatic service at Madrid?

Jack Wendover had told him of an ingenious method of communication invented by a married couple, who were spies in the pay of a foreign Government. She could hear him explaining it to Reginald Monkton, as she sat up in the dark, in that semiconscious state between dreaming and waking.

"They were clever. They wouldn't trust to ciphers or anything of that sort, when they were separated; it was much too commonplace. They sent each other photographs. The receiver cut the photograph down, and found between the two thicknesses of cardboard a piece of tissue paper, upon which was written the message that the sender wished to convey."

She could hear her father's hearty laughter, as he said: "Truly, a most ingenious method. Has that really been done?"

She had not been reminded of that for nothing, she felt sure. Why had this sudden recollection of an old conversation come to her in the dead of the night, if not for some purpose?