At Scotland Yard they acted upon my suggestion, and at once sent a wireless message to SeÑor Rivero in Madrid, telling him of the discovery of the notorious Mateo Sanz.

In the meantime my curiosity was further aroused by a note sent to me by Mrs. Tennison’s servant, Mrs. Alford, next day, saying that Doctor Moroni had called at Longridge Road and that, finding Miss Gabrielle absent, he had put to her a number of questions concerning myself.

“As I promised you, sir,” the woman wrote, “I pleaded ignorance of everything. He was apparently astonished to find my mistress and Miss Gabrielle away. He asked me for their address, but I replied that they were moving from place to place on the Continent. He seemed most annoyed, and went away.”

I wondered what was his object in going to Longridge Road, if not for the purpose of some further evil work. Though he pretended friendliness towards Gabrielle, yet I knew that he was her enemy, just as he was mine.

Moroni was in London, hence he would no doubt visit De Gex. Hambledon was unknown to Moroni, therefore he watched in Stretton Street on the following night, and in his work of observation he was assisted by Norah, who had been told something of the strange circumstances, though of course not the whole amazing story.

Just before eleven o’clock Harry and his fiancÉe arrived at Rivermead Mansions in a taxi and told me that they had seen Moroni arrive at Stretton Street about half-past nine. He was admitted by a new and rather supercilious man-servant—for Horton did not now seem to be in the great man’s employ.

“Ten minutes afterwards Suzor arrived,” Harry said. “Then about half an hour later Moroni came out.”

“I was passing the house slowly when he came down the steps muttering fiercely to himself in Italian,” Norah said. “He took no notice of me, for he seemed extremely angry and excited. Indeed, as he left, he glanced back at the house, his hands clenched, and he seemed to invoke a curse upon it.”

“By Jove!” I gasped. “That’s interesting! The precious trio have perhaps quarrelled!”

“Perhaps,” said Hambledon. “And as a lawyer I venture to predict that if they really have we shall, ere long, obtain some very interesting disclosures.”

Norah stayed and had some supper, for we were all desperately hungry, and later on Harry saw her back to Richmond.

Three days later, in consequence of a message sent to me from the Hotel Cecil, I went home early from the office to Rivermead Mansions, and had only been in five minutes when the door-bell rang.

On opening it I found my expected visitor, SeÑor Rivero.

“Ah! my dear friend!” cried the good-humoured police official, as he wrung my hand warmly. “So I have found you at last! The taxi-man made a mistake in the address and took me further down the road. Well, so you have been doing good business for us—eh? You have found Mateo Sanz!”

“Yes. I recognized him,” I said.

“I have just been with Superintendent Risden, of Scotland Yard, and we have seen our friend whom we have wanted for so long. He is quite unsuspicious. But I am told that two days ago he visited the house of Mr. De Gex.”

“Yes, he is his friend, just as Despujol was,” I remarked.

“But I cannot understand that!” Rivero declared. “It seems incredible that a person of such high standing as Mr. De Gex should number bandits among his friends!”

“I revealed to you the truth concerning De Gex when we were in NÎmes,” I said. “Even then you were half inclined to disbelieve it. Now you know the truth. The two business partners of Oswald De Gex, the Conde de Chamartin, of Madrid, and the Baron van Veltrup, of Amsterdam, have both died suddenly—and at the instigation of their unsuspected friend! It has been proved that Sanz introduced the tiny scrap of infected razor-blade into the Baron’s glove.”

“At De Gex’s instigation?—impossible!”

“De Gex was the only person to profit by the Baron’s death,” I pointed out. “He owed a large sum to the Baron over a financial deal, and by the latter’s death, and the destruction of certain papers, he now escapes payment.”

“But you surely do not allege that Mr. De Gex resorts to the use of this little known and unsuspected poison in order to secure his own ends!” cried the famous detective, as he sat opposite me in an easy-chair.

“When we know the truth—as I hope we may very soon—then you will be staggered,” I assured him. “At present you do not know the whole of the amazing story. For certain private reasons I have been unable to reveal it to you. But slowly, piece by piece, I have been steadily working upon the mystery of certain amazing occurrences at De Gex’s house in Stretton Street. By slow degrees, and after travelling up and down Europe, I have at last succeeded in finding just a streak of daylight through the impenetrable barrier so cleverly contrived in order to mystify and mislead me. If you desire to ascertain the great ramifications of the desperate plots conceived by De Gex and his friends, and take steps to combat them, it will be best to allow his accomplice Sanz further liberty. Keep vigilant watch, but do not allow him to suspect,” I urged. “He will no doubt go to Stretton Street again. Sanz, though a hired assassin as was his friend Despujol, should not be arrested yet, for the longer he remains at liberty the more extensive will be our information against the arch-schemer of Europe, Oswald De Gex.”

Rivero spent the evening with me. We dined at the Clarendon, across Hammersmith Bridge, and afterwards we idled in one of the foreign cafÉs near Piccadilly Circus.

He was in London with a warrant for the arrest of Mateo Sanz in his pocket. But at my suggestion he stayed his hand. Meanwhile Sanz, all unsuspecting, was being carefully watched, not only by two detective-sergeants from Scotland Yard, but also by two Spanish detectives whom Rivero had brought to London with him.

Two days later, in response to a message from Rivero, I called at the Hotel Cecil on leaving the office. He met me in the marble-paved entrance hall, and I noticed at once a grave expression upon his face.

“Come up to my room,” he said in French. “We can talk quietly there.”

In surprise I went with him up in the lift to the third floor where, in a bedroom which overlooked the Embankment and the Thames beyond, he turned suddenly to me and exclaimed, still in French:

“I am very troubled and mystified, Monsieur Garfield. When you made those curious allegations against Monsieur De Gex I confess that I laughed them to scorn, but I have to-day learned several facts which put an entirely fresh complexion upon the present circumstances. Last night Mateo Sanz visited De Gex again. The financier gave a musical evening, but after the departure of all the guests, Sanz called and was at once admitted to De Gex’s library.”

“Ah!” I exclaimed. “I know that room. I have sad cause to remember it!”

“He remained there till nearly two o’clock in the morning. Then he returned on foot to his hotel. My information is that on his walk back he was whistling to himself, as though in high spirits.”

“But that is surely no extraordinary circumstance!” I remarked. “Did I not tell you that De Gex is as friendly with Sanz as he was with Despujol?”

“I know. But in face of other facts I have learnt, the problem presented is an amazing one.”

As he spoke a tap came upon the door, and a page-boy handed in a card.

“Show the gentleman up,” Rivero said in his broken English.

“Here is someone who will relate some very strange facts. He is my friend Gonzalez Maura, an advocate who practised in Madrid before his appointment to our Consulate here. I called at the Consulate yesterday and saw him, when he related to me some curious facts which I have asked him to repeat to you. He is here for that purpose.”

A few moments later the page-boy ushered in a middle-aged, well-dressed, black-bearded man who bowed elegantly when we were introduced.

“Now, my dear friend,” exclaimed Rivero, when we were all three seated. “Will you please tell Mr. Garfield what you explained to me yesterday.”

“Certainly. I merely tell you what I know,” he replied in very fair English. “It is like this. Before I left Madrid I was very friendly with a country lawyer named Ruiz Serrano, who lived at Valladolid. For some reason the late Count de Chamartin took a great fancy to my friend, and constituted him his legal adviser, an appointment which brought him in quite a large income. To the lawyer of a great financier fees are always rolling in. The Count naturally took Serrano into his confidence and told him how, years ago, he had married the daughter of an Englishman in rather humble circumstances, living in Madrid. A daughter was born to them, but later he divorced his wife, who died soon afterwards, and then he married a lady of the Madrid aristocracy, the present widow. Apparently he made a will leaving the whole of his fortune to his daughter by his first wife—save for a small annuity to his second wife—and according to the will, on the death of his daughter the fortune was to go to his trusted partner, your English financier, Mr. Oswald De Gex.”

I sat staring at the stranger, but uttered no word, for I was reflecting deeply.

“SeÑor Serrano arrived in London a week ago, and came to consult me regarding the will, because it seems that the Count’s daughter—who came here to learn English, she having lived in Madrid all her life—is dead.”

“Hence De Gex has inherited the Count’s fortune?” I gasped. “What was the girl’s name?”

“Her name was, of course, Chamartin, but in obedience to her father’s wish, after the divorce she took her mother’s maiden name, and was known as Gabrielle Engledue.”

“Gabrielle Engledue!” I echoed. “Gabrielle Engledue!”