Words failing him, Joe could only take the card and incline his head in an old-fashioned gesture of thanks.

Stone raised a finger in teasing admonition. “I’m sure I don’t need to remind a lover of Horace that aequam memento rebus in arduis servare mentem.”

“Oh, I usually manage to remain calm, however rough the going gets,” Joe murmured. “This job demands it.”

As the door closed behind Reginald Stone, “Arrogant know-it-all!” Joe exclaimed under his breath, sliding the card away inside the case file. “And that professor’s no better!”

A tap on the door reminded Joe that he had neglected to name the next witness in line. The tap was followed by a floppy fair quiff and a pair of earnest brown eyes peering into the room.

“Jack Chesterton, sir. The colonel thought you’d want to see me next.”

“And he was right. Do come in!”

The young man settled down opposite Joe and produced a sheet of drawing paper from a slim attaché case. He handed it across the desk.

“I’m afraid I’m the spare wheel on this wagon, sir,” he said. “Everyone else had a part to play in the drama—and I must say, they did it splendidly! But I was left rather standing about. I took the opportunity of making an on-the-spot plan of the scene of operations while they were transporting the body and I worked it up over lunch. Scale diagrams are very much my thing, you see. I’m an architect.”

Joe studied the sheet. The site of the burial was marked, clearly set in its surroundings. A scale marked “estimated” helped him to judge the width of the riverbank and the grave’s precise location on it. Sketched from a viewpoint on the embankment, it was pinned down further by a triangulation involving the fixed points of Battersea Power Station and the Albert Bridge.

“I didn’t know the sketching convention for thick Thames mud, sir—not a substance we’re ever called on to treat as a foundation for our schemes—so I’ve left it blank.”

“It’s all perfectly clear, Mr Chesterton,” Joe said. “May I keep this for the file? My best officer couldn’t have done better. Splendid stuff!”

Chesterton smiled his satisfaction.

“Explain these markers for me, will you?” Joe asked, pointing with his pencil.

“On the left, which is the east as we’re on the north bank, is a rotting old breakwater—revêtement, whatever you want to call it. Long past its useful life. And on the right, the rounded object is an overturned boat in similar condition.”

“It’s above the waterline?”

“Yes. It was perfectly dry. The professor sat on it. Reluctantly—he claimed it stank of rotting seaweed. We put all our gear at his feet for safe keeping.”

“Any sign of habitation?”

“Rats, you mean?” Chesterton grinned. “Prof Stone made rather a show of banging about along the keel to frighten off any rodents …” His voice trailed away then resumed, “But, hang on! When we were looking for a place to park our bags, I cleared out some rubbish …” His eyes met Joe’s.

“And found the source of the pong. Chicken bones! And a paper bag—one of those little cornet-shaped ones—an empty one that had contained brown shrimps by the look and smell of it.” And, excitedly: “They weren’t rat-nibbled. You’re right, sir! Someone sleeping rough? He wasn’t there when we were. But he could have been sheltering under the boat when the body was buried, don’t you think? I’m assuming that the deed was done under cover of darkness.”

Joe agreed and thought that if he just sat there quietly this team would solve his problems for him.

“Mr. Chesterton, may I ask you to go and find Inspector Orford and tell him to come in here. I’d like you to outline your theories for him.”

Chesterton shot to his feet. “Orford? He’s in the waiting room keeping us all plied with coffee and stopping everyone from scragging Prof Stone. I’ll get him.”

Orford was impressed. He beamed. He took out his pencil and scribbled a few notes on Chesterton’s plan. “I was planning to have the lads down there with measuring tapes and all the paraphernalia at first light. But before they run loose churning up the mud, I’ll send in a couple of discreet blokes—one of whom might be me—to keep watch on that boat. See if we can catch ourselves a witness. Another one,” he sighed with mock weariness. “The more, the merrier, I expect.”

“Only three to go,” said Joe. “I’ll take the colonel and his men in one job lot. Mr. Chesterton, you’ve been of great help. Could you, as you leave, ask Swinton to come in?”

SWINTON SETTLED DOWN on a chair, flanked by his Suffolk gardeners.

Sam and Joel gazed about them, recording yet another experience of the city with wide-eyed disbelief. For men whose sole previous contact with the law of the land had been the village bobby’s boot up the bum as they fled an orchard with pockets full of scrumped apples twenty years before, their presence in the office of a top man at Scotland Yard was overwhelming. And, in some ways, disappointing. Not at all what they’d expected. No clanking cell doors, no manacles, no screams, not even many men in uniform. Their tea had been served from a trolley by a flirty old biddy in a white pinny. In the top bloke’s office there were more surprises. All here was neatness and order with pictures on the walls like someone’s front parlour. A telephone stood to attention on an expanse of gleaming mahogany desk. Across the desk a smiling young gentleman in a smart city suit greeted them by name and they listened with disbelief as he told them who he was.

He began his business by thanking the pair for their efforts and the speed with which they’d worked to secure a vulnerable corpse.

“Weren’t nothin’ else we could ’a done,” said Joel modestly. “Blowed if we was goin’ to let that old river have her!”

“Well, you’ll be pleased to hear that we have a very strong line of enquiry going at the moment and we’re expecting very soon to be able to give your girl an identity. We’ll let you know her name before much longer.”

This was what they were anxious to hear. Two more victims, Joe thought, ensnared by the dead girl whose grip showed no sign of loosening.

“We’ll be glad to give our statements, Commissioner,” the colonel said. “And if there’s anything else we can supply—anything at all—you know where we are. We’ll stay on in London until someone sounds the all clear. Pleased to be of help.”

“A few questions, for the moment,” Joe said. “I was wondering how you got yourselves into this predicament. Tell me—it was Miss Herbert’s selection of terrain, was it? This stretch of riverbank?”

“Not exactly. In fact I take full responsibility for the choice of that patch. Hermione was determined to stage her dowsing experiment and, having been consulted, I cast a soldier’s eye on the problem. Three things recommended the Chelsea reach to me.

“One: ease of digging. Mud not pleasant underfoot but quickly moved with the right spades.

“Two: strong possibility of making a find. The banks of the Thames are a rich hunting ground. The museums of London are stuffed with items brought to light by a swirl of those dark waters. From very ancient times up to the day before yesterday. And that particular bit seems to have been in use in the Roman-British period, which is always of interest. Certainly of interest to Reginald Stone. He, for one, was quite keen when I proposed it, though I’m sure he would deny any enthusiasm if you asked him. Yes, Reginald had a definite gleam in his evil old eye!”

Ambushed by a stray thought, Swinton unlocked his eyes from Joe’s. The clipped ops-room tone was abandoned as he added: “Yes … he leapt straight on to it, you might say. The coin, I mean. He turned that riverbank into a lecture theatre.” He snorted with laughter. “Had my lads gripped all right, didn’t he?”

Sam and Joel grinned and nodded agreement. “Never knew that about coins!”