With that dramatic suddenness created by fog, a constable flashing an amber torchlight stood in their path.

“Well?” Tillottson said, leaning out of the window.

“This is as far as you can drive, sir.”

“Where’s Cape?”

“T’other side, sir.”

They got out. Close on their left hand the fog-masked weir kept up its anonymous thunder. They followed the constable along the tow-path to the flight of steps that led up to the main bridge.

“All right,” Tillottson said. “Get back to your point.”

As they groped their way over the bridge a car crept past them filled with revellers engaged in doleful song.

The constable stepped into its path and waved his torch.

“Hullo—’ullo—’ullo,” shouted the driver. “Anything wrong, Officer?”

“Just a minute, if you please, sir.”

“Our Breath is as the Breath of Spring,” someone in the back seat sang dismally.

“May I see your licence, sir?”

When this formality was completed Alleyn and Tillottson moved in. Had they, Alleyn asked, seen a solitary woman? They replied merrily that they’d had no such luck and emitted wolf-like whistles. Alleyn said: “If we weren’t so busy we’d have something to say to you. As it is, will you pull yourselves together, proceed on your silly journey, stop if you see a solitary woman, and address her decently. If she’s got a strong American accent, offer her a lift, behave yourselves and drive her to the nearest police stop or police station, whichever comes first. Do you understand?”

“Er — yes. Righty — jolly-ho. Fair enough,” said the driver, taken aback as much by Alleyn’s manner and voice as by what he said. The passengers had become very quiet.

“Repeat it, if you please.”

He did.

“Thank you. Drive carefully. We’ve got your number. Good night.”

They crawled away.

Bailey and Thompson and their driver loomed up and the whole party inched along until they found the top of a flight of steps going down to the lock.

“What can have got into her?” Fox mused, not for the first time.

“Fear,” said Alleyn. “She was terrified. She’s tried to do a bolt. And succeeded, blast it. The Skipper must have delayed—hallo, here we are. That’s the roof of the lockhouse down there. Come on and for God’s sake don’t let’s have any falling into the lock. Easy as we go, now.”

They felt their way down the steps to the tow-path.

“Cape!” Tillottson shouted in a terrible voice.

“Here, sir.”

He was wretchedly waiting where he had been told to wait: between the lock and the lockhouse. The fog down here was dense indeed and they were upon him almost before they saw him. He seemed to be standing to attention and expecting the worst.

“Ever heard of a Misconduct Form?” Tillottson ominously began.

“Sir.”

“Superintendent Alleyn’s got something to say to you.”

“Sir.”

Alleyn said: “What happened, Cape?”

There had, he said, been a commotion on board the Zodiac. He couldn’t see anything much because of the Creeper but he heard the Skipper’s voice asking what was wrong and a woman taking on a fair treat, shrieking: “Let me go. Let me go.” He went down to the moorings and called out: “What seems to be wrong there?” but as far as he could make out the happening was on the far side. And then one of the gentlemen on board came round the deck and asked PC Cape where he was and said he’d better come on board and get things under control like. He could hardly see a thing except that there was a gap between the edge and the gunwale. He couldn’t see the gentleman either but said he had a very loud voice.

“Go on.”

The loud voice said he could jump for it and as he could just make out enough for that he did jump and came aboard in a flounder and nearly lost his helmet. Alleyn gathered that a sort of blind search had set in under circumstances of the greatest possible confusion. Cape had proceeded with outstretched arms doing a breast stroke action, to the starboard side which was the farthest removed from the tow-path. He had bumped into a number of persons and had loudly demanded that everybody should keep calm.

A strange disordered mélée now took place in the greatest possible confusion. Presently it occurred to Cape that the woman’s voice could no longer be heard. He had got alongside the Skipper and they had, between them, rounded up the passengers and herded them into the saloon where after a good deal of milling about and counting of heads, Miss Hewson’s head was found to be missing.

By this time the policemen on the pub side of the river had become alerted and started to cross the bridge.

Cape and the Skipper went through the cabins and searched the craft. All available lights were switched on but were not much help on deck where the fog was now of the pea-soup variety.

Caley Bard and Dr Natouche bore a hand and the Skipper had evidently behaved very sensibly. When it was certain that Miss Hewson was not in the Zodiac, Cape got himself ashore and blew his whistle. He and his colleague now met, poked uselessly about in the fog and settled that while Cape got through to Tollardwark his mate should alert by walkie-talkie the other men on duty in the vicinity.

Alleyn said: “Very well. Where’s the Zodiac?”

“The boat, sir?” Cape ejaculated. “I beg pardon, sir?”

“Where’s the bloody lock, for pity’s sake.”

“The lock, sir?”

“Find the lockhouse and stay by it, all of you.”

Alleyn inched along the tow-path. A lighted window loomed up on his left. The lockhouse. He faced right, stood still, listened and peered down into a blanket.

“Hallo? Zodiac?” he said very quietly.

“Hallo,” said a muted voice below his feet.

“Skipper?”

“That’s right.”

“Show a light, can you?”

A yellow globe swam into being far below.

“You did it, then? You and Tom?”

“And the Lock himself. Talk about stable-doors! It was a job in this muck but here we are.”

“All present?”

“Except for her.”

“Sure?”

“Dead sure.”

“No idea, of course, which way she went?”

“No idea.

“And Mrs Tretheway’s sleeping at the lockhouse?”

“Yes.”

“Good. You’re very quiet down there.”

“They’ve gone to bed. I waited for it.”

“Do they know where they are?”

“Not when I saw them. They will.”

“They could scramble up and out, of course.”

“They’re in their cabins and they can’t get ashore from there. Have to come up on deck and young Tom and I are keeping watch.”

“Splendid. Stay put till you hear from us, won’t you?”

“Don’t make it too long,” the voice murmured.

“Do our best. Good night.”

Alleyn returned to the lockhouse. He and the other six men were admitted by the keeper and crowded into the parlour.

“Well,” Alleyn said. “Search we must. Any chance of this lifting?”

Not before dawn, most likely, said the lock-keeper but you never knew. If a wind got up, she’d shift.

“It’s essentially a river mist, isn’t it?” Alleyn said. “Miss Hewson may still be milling round in it or lying doggo. If she managed to get above it she’ll be on the move. All we can do is follow the usual procedure.” He looked at the Tollardwark constable. “You’d better keep within hailing distance of Mr Tillottson, Mr Fox and me. You’ve got radar and we haven’t. We’re going to find our way up to the wapentake. Br’er Fox, would you work out to my right. Bert, if you’d keep going beyond that and take the driver out on your own right wing. Bailey and Thompson, you take the left wing. Near the roadside hedge if you could see it. She may be anywhere: under the hedge in the Wapentake Pot or a quarter of a mile away. As little noise and talk as possible. The rest of this unspeakable terrain we leave to the men already alerted.”

He looked at the wretched Cape.