As John May and Maggie Armitage reached the mouth of the tunnel, they threw away caution and began calling for their friend. Their voices returned unanswered from the curving walls.

“He has to be inside,” said May, “his tracks lead to the entrance. Stay out here and look after the boy. I’ll go in.”

As he stepped into the blanket of the dark, he heard it, the distant ring of the approaching train. “Arthur, are you hurt?” he called. “Listen to me carefully. Madeline Gilby is a very dangerous woman. The man she insists is hunting her is Johann Bellocq, and he’s actually trying to stop her. There are no pictures of murder victims, no forged passports. Arthur, answer me!”

He could feel the weight of the train on the tracks, the steady displacement of air in the far end of the long tunnel, the faint crackle of electricity. A dim light appeared on the wall of the first bend. As it slowly increased in brightness and moved down, he saw what appeared to be a bundle of rags lying across the tracks. As he watched, it flinched like an animal caught in the coils of a snake, and he realised that he was looking at his partner, trapped with Madeline Gilby’s limbs twisted around him. Bryant’s boots kicked out in a burst of gravel, and he twisted his head to look plaintively around for help.

May dropped to his side and pulled at an arm, but Madeline’s clutch tightened, rolling Bryant further onto the centre of the track. “You’ll kill us all,” May told her. “We can get you help, Madeline. It doesn’t have to end this way.”

Ahead, the lights of the train grew brighter as it coasted the bend of the tunnel in a roar of sparking steel.

He tried to prise open her hands, but the muscles in her fingers and arms had locked with steely rigidity. Bryant kicked and wriggled, but was rapidly losing strength. Gilby was on top of him now, knotted around his body in a death grip that nothing could loosen. Braced against the track, May pulled at them in vain.

“Let me,” said Maggie, hopping across the tracks and grabbing Bryant’s attacker from the other side. Madeline Gilby let out a sudden piercing yell and threw out her limbs as wildly as if she had been electrocuted. Released and able to breathe once more, Bryant let out a gasp.

May pulled hard, dragging his partner across the rail and up against the wall. He reached out a hand to Madeline, shouting for her, but she crawled further away, turning to face the explosion of light and noise.

May caught sight of Madeline’s pale face one last time; her widening eyes were staring into the long white shaft of light that emanated from the front of the engine in the corridor of the tunnel. She looked quite calm, as if she was glad to be finally faced with the prospect of meeting her Maker.

A moment later, the duo watched as the flashing yellow panels raced past them, and the carriages started to slow with the braking of the train. When it had finally passed, there was no trace left behind of Madeline Gil by.

Maggie Armitage had flattened herself against the opposite wall of the tunnel. Her arms were splayed and her hair had been shocked into a vermilion sunburst around her head, like Struwwelpeter.

“What did you do to make her let go?” called May as he pulled Bryant to his feet. “Stick her with an evil enchantment?”

“No, a hatpin,” replied the white witch breathlessly. “Every bit as effective. At least she didn’t have to go towards the light. It came to her.”

“The final white corridor,” said May, taking her hand. “Come on, you two. Let’s get out of the dark.”

They stood neatly in line, the seven of them, Meera Mangeshkar and Colin Bimsley, Dan Banbury and Giles Kershaw, Raymond Land, April May and Janice Longbright.

Meera had decided to work on an expression that could not be construed as a scowl, and had loosened her tied-back hair so that it glossily framed her face. Longbright had shown her how to administer lipstick, although teaching her to stop flinching as it was applied had proven tricky.

Colin had polished his shoes and was proudly wearing his father’s old police tie. The legendarily clumsy PC was under strict instructions to keep his hands by his sides and not attempt anything more complicated than taking one pace forward or back.

Dan was dressed in the too-tight grey Ben Sherman suit he always wore to work, but his wife had forced him to don his only white shirt that took cuff links.

Giles was wearing his Eton tie, a lurid red carnation he had filched from April’s garage flowers and a baggy blazer that made him look like a Henley Regatta captain.

Raymond Land had ditched his cardigan and opted to stretch a yellow striped shirt across his paunch, slicking back his receding locks with his son’s hair gel so that he resembled a provincial advertising manager, or possibly a pimp.

Having escaped from the storeroom in which he had been shut, Crippen threaded his way through Land’s legs and thought about taking a pee, but wisely decided against it.

April wore a simple black dress and matching shoes, with pearl earrings and a single strand of black pearls that had been bequeathed to her by her grandmother.

Janice Longbright was sporting a pair of high-heeled court shoes that had once belonged to Alma Cogan, the fifties chanteuse, and a seashell hair slide in the style of Dorothy Lamour. She was still wearing the red woollen two-piece suit she had borrowed to infiltrate the Circe Club earlier that day.

They had all done what they could to look smart, and the net result was appropriately peculiar. But on this afternoon, at this moment, they all felt part of an alternative family, the invisible connections of friendship joining them to one another more surely and steadfastly than any blood tie. For once, they were individuals united as one.

The offices of the Peculiar Crimes Unit had never looked clean, but at least all of the unfinished cabling, Bryant’s dubious personal belongings and Crippen’s litter tray had been shoved into storage cupboards. April had indulged her passion for neatness, placing fresh-cut flowers on every desk and arranging every file, every chair, every pen and piece of paper in pristine symmetry. The unit wasn’t quite fit for a queen, but it would do for a princess.

April coughed nervously. Colin checked his breath and dug for a mint. Giles stole a surreptitious glance at his watch. Dan adjusted his boxers through his trousers. Janice pushed an errant coil of hair back in place and peeked at the opening door. Crippen rolled over onto his side and fell into a light doze. It was so unnaturally quiet that they heard the central heating thermostat turn itself off.

Rosemary Armstrong entered in a display of stiff hair and thick ankles, dressed in a peculiarly Tatler-ish arrangement of floral silk scarves that made her look like an ambulatory sideboard centrepiece from one of the less beloved National Trust homes. In an attempt to put everyone at ease, she sported an official smile that made even the cat wake up and move away.

Longbright leaned back into line with the others, disappointed to see that it was the Princess’s assistant and not her bosses. The last she had heard, Arthur Bryant and John May had been collected by train, then a Royal Navy helicopter, to get them en route to Mornington Crescent for five o’clock, but it was now twelve minutes past and they were cutting it very fine indeed.

“The Princess has just arrived,” said Rosemary, cautiously sniffing the air. “Everything shipshape here, yes?”

Longbright peered out through the sleet-stained crescent window and saw the black Bentley parked in the cordoned-off street outside. As she watched, Leslie Faraday and Oskar Kasavian alighted onto the strangely clean pavement in tight black suits and narrow ties, looking like agents of Beelzebub.