It was undoubtedly cipher, but whether a simple or abstruse one Foyle was in no position to judge. He had an elementary knowledge of the subject, but he had no intention of attempting to solve it by himself. There were always experts to whom appeal could be made. A successful detective, like a successful journalist, is a man who knows the value of specialists—who knows where to go for the information he wants. That meaningless jumble of letters could only be juggled into sense by an expert. Foyle nevertheless scrutinised them closely, more as a matter of habit than of reading anything from them. They were—

UJQW. BJNT. FJ. UJM. FJTV. UIYIQL. SK. DQUQZOKKEYJPK. ANUJ. M.Q. NG. N. AYUQNQIX. IGZ. ANUJ. SIO. IGZ. SMPPN. RT. 12845 HGZVFSF.

"We'll let Jones have a go at that," he said. "Anything else now?"

Some one handed him the knife that had been thrown at him on the landing and a curious leather sheath that had been picked up near the bed. From the bottom of the sheath depended a leather tassel. Foyle looked it over and failed to discover any manufacturer's name. He slipped the weapon into his pocket with the mental reflection that it looked Greek. The search went on from attic to cellar, and profuse notes were taken of everything found, with its exact position. The elaborate trouble taken by these men to describe minutely in writing every little thing would have seemed absurd to any one not versed in the ways of the Criminal Investigation Department. Yet nothing was done that was not necessary. An error of an inch in a measurement might make all the difference when the case came on for trial.

Foyle and Green left the house in charge of the divisional man. Already a description had been circulated of the man they had failed to surprise; but as neither had caught more than a glimpse of a shadowy figure in the darkness, they had had to rely on the descriptions given by Israels and his wife. And even if that estimable pair had really tried honestly to give a fair description of the man—which the detectives thought was extremely doubtful—there could be little hope that it was accurate. If the average man tries to describe the appearance of his most intimate friend and then asks a stranger to identify him, he will realise how misleading such descriptions may be even at the best of times. Yet the Criminal Investigation Department had to work with such material as they had.

Heldon Foyle was very silent as they trudged side

by side out of Whitechapel into the silent City streets—for there are no taxicabs to be found in the East End at such hours. The case was developing; but though he was beginning to have a hazy glimpse into some of its workings, there was much that remained a mystery to him. His questionings of Israels had satisfied him that the man who had escaped was neither Grell nor Ivan. He could not blame himself for not effecting an arrest. Looking back over the night's events, he could not see that he could have taken further precaution. If he had taken more men the escape would have occurred just the same over the roofs, for he would still have felt it his duty to question Israels. He could not have foreseen that the ready-witted Lola was there, nor that she should have so ingeniously given the alarm. The luck had been against him.

Nevertheless he had gained an important fact. Lola was in London and was obviously acting in concert with Grell. It was easier to look for two persons than one. Sooner or later he would lay hands on them and solve the mystery of the murder. He clenched his fists resolutely as his thoughts carried him away. Meanwhile there was the cipher. If that could be de-coded it might be valuable.

Green's voice broke in upon his thoughts.