The question of the caves intrigued Michael more than any feature the case had presented. He bethought himself of Mr. Longvale, whose knowledge of the country was encyclopædic. That gentleman was out, but Michael met him, driving his antique car from Chichester. To say that he saw him is to mistake facts. The sound of that old car was audible long before it came into sight around a bend of the road. Michael drew up, Longvale following his example, and parked his car behind that ancient bus.

“Yes, it is rather noisy,” admitted the old man, rubbing his bald head with a brilliant bandana handkerchief. “I’m only beginning to realize the fact of late years. Personally, I do not think that a noiseless car could give me as much satisfaction. One feels that something is happening.”

“You ought to buy a ⸻” said Michael with a smile, as he mentioned the name of a famous car.

“I thought of doing so,” said the other seriously, “but I love old things⁠—that is my eccentricity.”

Michael questioned him upon the caves, and, to his surprise, the old man immediately returned an affirmative.

“Yes, I’ve heard of them frequently. When I was a boy, my father told me that the country round was honeycombed with caves, and that, if anybody was lucky enough to find them, they would discover great stores of brandy. Nobody has found them, as far as I know. There used to be an entrance over there.” He pointed in the direction of Griff Tower. “But many years ago⁠—”

He retold the familiar story of the landslide and of the passing out of two companies of gallant knights and squires, which probably the old man had got from the same source of information as Michael had drawn upon.

“The popular legend was that a subterranean river ran into the sea near Selsey Bill⁠—of course, some distance beneath the surface of the water. But, as you know, country people live on such legends. In all probability it is nothing but a legend.”

Inspector Lyle was waiting for the detective when he arrived, with news of a startling character.

“The advertisement appeared in this morning’s Daily Star,” he said.

Michael took the slip of paper. It was identically worded with its predecessor.

“Is your trouble of mind or body incurable? Do you hesitate on the brink of the abyss? Does courage fail you? Write to Benefactor, Box⁠—”

“There will be no reply till tomorrow morning. Letters are to be readdressed to a shop in the Lambeth Road, and the chief wants you to be ready to pick up the trail.”

The trail indeed proved to be well laid. At four o’clock on the following afternoon, a lame old woman limped into the newsagent’s shop on the Lambeth Road and inquired for a letter addressed to Mr. Vole. There were three waiting for her. She paid the fee, put the letters into a rusty old handbag and limped out of the shop, mumbling and talking to herself. Passing down the Lambeth Road, she boarded a tramcar en route for Clapham, and near the Common she alighted and, passing out of the region of middle-class houses, came to a jumble of tenements and ancient tumble-down dwellings.

Every corner she turned brought her to a street meaner than the last, and finally to a low, arched alleyway, the paving of which had not been renewed for years. It was a little cul-de-sac, its houses, built in the same pattern, joined wall to wall, and before the last of these she stopped, took out a key from her pocket and opened the door. She was turning to close it when she was aware that a man stood in the entrance, a tall, good-looking gentleman, who must have been on her heels all the time.

“Good afternoon, mother,” he said.

The old woman peered at him suspiciously, grumbling under her breath. Only hospital doctors and workhouse folk, people connected with charity, called women “mother”; and sometimes the police got the habit. Her grimy old face wrinkled hideously at this last unpleasant thought.

“I want to have a little talk with you.”

“Come in,” she said shrilly.

The boarding of the passageway was broken in half a dozen places and was indescribably dirty, but it represented the spirit of pure hygiene compared with the stuffy horror which was her sitting-room and kitchen.

“What are you, horspital or p’lice?”

“Police,” said Michael. “I want three letters you’ve collected.”

To his surprise, the woman showed relief.

“Oh, is that all?” she said. “Well, that’s a job I do for a gentleman. I’ve done it for years. I’ve never had any complaint before.”

“What is his name?”

“Don’t know his name. Just whatever name happens to be on the letters. I send ’em on to him.”

From under a heap of rubbish she produced three envelopes, addressed in typewritten characters. The typewriting Michael recognized. They were addressed to a street in Guildford.

Michael took the letters from her handbag. Two of them he read; the third was a dummy which he himself had written. The most direct cross-examination, however, revealed nothing. The woman did the work, receiving a pound for her trouble, in a letter from the unknown, who told her where the letters were to be collected.

“She was a little mad and indescribably beastly,” said Michael in disgust when he reported, “and the Guildford inquiries don’t help us forward. There’s another agent there, who sends the letters back to London, which they never reach. That is the mystery of the proceeding. There simply isn’t such an address at London, and I can only suggest that they are intercepted en route. The Guildford police have that matter in hand.”

Staines was very worried.

“Michael, I oughtn’t to have put you on this job,” he said. “My first thoughts were best. Scotland Yard is kicking, and say that the meddling of outsiders is responsible for the Headhunter not being brought to justice. You know something of interdepartmental jealousy, and you don’t need me to tell you that I’m getting more kicks than I’m entitled to.”

Michael looked down at his chief reflectively.

“I can get the Headhunter, but more than ever I’m convinced that we cannot convict him until we know a little more about⁠—the caves!”

Staines frowned.

“I don’t quite get you, Mike. Which caves are these?”

“There are some caves in the neighbourhood of Chichester. Foss knew about them and suspected their association with the Headhunter. Give me four days, Major, and I’ll have them both. And if I fail”⁠—he paused⁠—“if I fail, the next time you say good morning to me, I shall be looking up to you from the interior of one of the Headhunter’s boxes!”