“Yes,” said Ronnie. “This secret place of meeting is known to the spies of Germany as ‘Number Three.’ From here certain of the clever activities of the invisible hand of Germany are frequently directed, as from other centres; Mark Marx is a clever adventurer who used to be the assistant director of the enemy’s operations in this country. Apparently he has returned to London to resume his sinister activities against us. He acts directly under the control of the head of Germany’s secret service in this country, that shrewd, clever, and influential person who hides his identity beneath the official description of ‘Number Seven.’”
“Then ‘Number Three’ is the headquarters of ‘Number Seven’--eh!” asked the ex-detective in a whisper.
“Exactly. That some devilish conspiracy is now afoot is quite certain. Our duty is to discover and to thwart it. I was secretly warned that Mark Marx had returned, and now, knowing that it is so, I must take adequate precautions.”
“But can’t we endeavour to ascertain what is in progress here to-night, Mr. Pryor?” suggested Cranch.
Pryor and his companion kept vigilant watch till far into the night when, about two o’clock in the morning, a big closed motor-car suddenly came along the road, pulling up a little distance from the house. The driver, a tall, thin man, alighted and waited for some moments, when the two men, Marx and Klitz, _alias_ Knowles, emerged carrying between them a small but heavy leather travelling trunk and, assisted by the driver, placed this on top of the car. Then the two men entered and drove rapidly away.
“That car may come again to-morrow night,” remarked Pryor. “We must lay our plans to follow it.”
Next night, Pryor having ascertained the identity of the friend who had warned him of Mark Marx’s return to England, he and Cranch were again at the same spot beneath the stunted lilac-bush. Round the corner, in Villa Street, at a little distance away stood Ronnie’s closed car with Beryl Gaselee in charge, the latter wearing the cap and dust-coat of a war-time _chauffeuse_.
Hour after hour they waited until dawn broke. But as no one came to that house known as “Number Three,” they were compelled at last to relinquish their vigilance.