She didn’t quite click her heels but Joe almost expected to hear it.

‘Very well. We’ll leave it. But I’m not satisfied with your explanation and will come back to it. I shall need to know precisely what brought you to this room at such an unlikely hour to see someone you say you were not acquainted with. Now, we need to establish without further delay who is her next of kin.’

‘I could just tell you but perhaps you’d rather read the details from her diary which is in the bedroom. She lives in Surrey with her mother. Not married, of course.’

At a nod from Joe, Westhorpe went into the bedroom, emerging with a small black notebook. ‘Here we are . . . Mrs Augustus Jagow-Joliffe, King’s Hanger, near Godalming. There’s a telephone number. Dame Beatrice has a flat of her own, I think . . . yes . . . here’s the address – it’s in Fitzroy Gardens.’

She handed the book to Joe and he put it in his pocket.

‘Where would you like me to start, sir? Shall I make a sketch of the crime scene?’

‘Hold on, Westhorpe. That’s a job for whichever inspector they’ve supplied us with. You can make a start on her personal effects. An inventory, if you like.’

Westhorpe just managed not to roll her eyes in disbelief. ‘Very well. I’ll start in the bedroom as that’s where most of the effects are and leave the field clear for the attentions of a superior officer.’

Joe opened his bag and took out a notebook and a pencil. ‘Here, use this.’ He stood in the doorway watching as she set about making her inspection. He had expected her to make at once for the wardrobe or the chest of drawers but she stood by him, surveying the room.

‘First of all, the bed’s been turned down so a member of the hotel staff has been in the room this evening though it will probably have been well before the time we’re interested in. They usually come in about nine o’clock . . . though I did see a maid pushing one of those little chariots they have with bed linen and towels and so on down the corridor when I got up here the first time.’ She looked thoughtful.

‘Indeed? Was she coming towards the room or going away?’

‘Hard to tell. She was right at the other end. Going away, I’d say. When I came out again, there was no sign of her. If she’d been there I would have sent her down with a message.’

She opened the notebook at a clean page and prepared to write. ‘I’ll start with what she’s got on, shall I? Evening dress. I’ll leave the interesting condition of same to others. No gloves, you see, sir. They’re over there on that table. Neatly folded, worn but unstained. First thing a woman does when she gets back to her room is take off her gloves and kick off her shoes. But she still had her shoes on – did you notice? Could have been expecting someone? Perhaps her evening wasn’t over? She hadn’t started to draw a bath.’

‘Just list the items, please, Westhorpe.’

‘She’s put her gloves down with her evening bag.’ Without compunction, Westhorpe picked up the delicate, bead-sewn satiny confection and checked the inside. ‘Lanvin. Contents just what you’d expect for an evening out. Female things!’ She held it under Joe’s nose. ‘Small amount of cash . . . oh, and a couple of keys. Door keys.’

Joe took them and slipped them into an envelope. Westhorpe noted this.

He followed her through to the bedroom. ‘Wardrobe first, I think.’ She swung the doors back and began her list, commenting on the items she saw. ‘Not much here. I assume she had only booked in for two nights.’

‘Why do you say “only two nights”?’ He had already ascertained as much from reception.

‘It’s a two-day wardrobe. Her travelling suit – of good tweed with a matching blouse which presumably she was wearing when she came up this morning . . . and a spare blouse for the journey back. Two day dresses . . . both by Captain Molyneux . . . yes, she would wear Molyneux. Two hats, one chestnut felt, one black grosgrain with a brim. A fur jacket. One pair of walking brogues and a pair of lighter shoes in kid. That’s it.’

She moved to the dressing table. ‘One ivory-backed hairbrush and a leather trousse for toiletry items. Hair pins. Packet of “quelques fleurs” powder leaves.’

Joe’s interest sparked as she finally moved to the drawers, the searching of which was the reason for her being here, getting under his feet, he reminded himself. She took off the police cape and put it down carefully at the bottom of the bed. ‘Do you mind, sir? It’s really rather hot in here. Central heating. Wonderful, isn’t it? And, after all, the reason for wearing protective covering seems to have evaporated. Now . . . two camisole sets, one lawn, one . . . ooh!’ To his surprise, she shook out and held up to his embarrassed gaze a slippery-looking undergarment in magenta.

‘Silk,’ she commented. ‘The real thing, not crêpe de Chine.’ And, examining the label, ‘From a very exclusive shop – Ma Folie – in Wigmore Street.’ She folded it deftly and replaced it in the top drawer.

‘Westhorpe, you don’t need to demonstrate the lady’s wardrobe,’ said Joe uncomfortably.

With a slight smile of triumph she continued her list, calling out the items as she wrote. ‘Three pairs of silk stockings, two still in packets. Two slips of oyster satin, six lawn handkerchiefs.’

Irritated that his attention was being distracted by laundry lists of peripheral importance to his enquiry, Joe was edging quietly back towards the murder room when she stopped him with an excited call. ‘Oh, this is interesting!’ She was extracting a small black leather box bearing heraldic gold insignia from the bottom of the underwear drawer. ‘You ought to see this, sir!’

‘What is it?’

‘Well, it’s not her secret store of cachous!’

Intrigued by his constable’s reaction and the knowledge it revealed, Joe watched, fascinated as she opened the box and showed him the contents.

‘Ha! A Dutch cap! And from a very recherché and vastly expensive establishment. The Gräfenberg Clinic. Nothing but the best for Dame Beatrice, you’d say!’

She wrote up the entry in her notebook even adding, Joe noticed, the serial number on the bottom of the box. ‘Ah!’ she said.

‘Yes, Westhorpe?’

Tilly smiled in a knowing way. ‘There are two such clinics, one in Harley Street, the other in Berlin. This is from the Berlin branch. Very discreet! Someone of Dame Beatrice’s notoriety would never, of course, be seen crossing the London threshold of such a place, let alone Dr Stopes’ clinic in Whitfield Street. Far too near home.’

Joe was finding Westhorpe’s asides and insights informative – as, indeed, she had promised – and for the moment he held in check his urge to call her to heel and remind her of her lowly professional position. All the same, he was uncomfortable with the role she was assuming for herself and he was relieved when a tap on the door announced the arrival of – he hoped – an inspector. He went to the door, finding, to his annoyance, that Westhorpe had joined him and was hovering at his elbow still holding the box.

At the sight of them, the man standing outside looked up instinctively to check the number on the door. A middle-aged man with an eager expression underlined by a flamboyant moustache, he was wearing a trench coat over a brown tweed suit. In one hand he held a bowler hat and in the other a large black leather bag. He was trying very hard not to laugh.

‘You have the right room,’ said Joe curtly.

‘Good evening, sir. Oh, er, I say,’ he said, swallowing a smile. ‘Awfully sorry, sir . . . no one thought to warn me that this was a black tie occasion . . . miss.’ He nodded politely at Westhorpe.

‘Even the corpse is in evening dress, you’ll find, Cottingham. Join the party. You’re very welcome. I must introduce you to Constable Westhorpe who is seconded to our unit. She’s, um, working under cover. At Sir Nevil’s suggestion. Westhorpe, this is Inspector Ralph Cottingham. Ex-Guards officer so no doubt you’ll feel free to be rude to him too.’