Sherlock snatched the candle out of John's hands and charged up the staircase with it, the flame streaming out like a tiny comet. By the time John and Lestrade had made their way up, Price fumbling along behind, Sherlock was in action, flinging open the closed bedroom doors and searching around in the darkness beyond them. He emerged from the third bedroom from the top of the stairs just as John reached the landing.

"Anything?" John asked him hopefully.

Sherlock shook his head. In the light of the candle, his sharp cheekbones and almond-shaped eyes made him look almost ghoulish. "Nothing."

"Well, keep looking, then." Lestrade now had his mobile phone out and was using it as a torch. He opened the next door unconcernedly and stepped inside. "We all heard it, so something had to have made it, for God's sake."

"What is it you were saying about ghosts before, gentlemen?" Price asked, a little smugly. But Lestrade, re-emerging from the second bedroom door and reaching out for the door handle of the third, scoffed.

"I'm not worried about ghosts," he said. "I'm a bit worried a real human being was up here getting themselves smacked over the head, 'cause that's exactly what it sounded like. John?"

John had by now also got his phone out and had just emerged from the fourth room along. He shook his head.

"Rats," Sherlock suggested a little weakly, running his hand through his hair and looking around as if he expected the solution to be written on the wallpaper. "Just rats..."

"Yeah, really heavy rats," John agreed.

"We've never heard the natural sounds this house makes at night, and we still can't eliminate the possibility of fraud," Sherlock said crossly. "We saw this afternoon that the house has strange acoustics, and can't be..."

He trailed off. From the kitchen directly underneath him, there was a high, tinny clanging noise, echoing sharply in the still house.

"All right," Sherlock said loudly. "That really is the rats. The servant's bells are suspended on old wires that run inside the walls. The rats run along the wires, and their weight is what sets off the bells. Mabel Smith told me that tonight."

"I think I'd prefer the ghosts, if I'm honest," John muttered. In the three years he'd spent in Afghanistan, he'd largely got used to the spiders and cockroaches and scorpions and snakes. But he had never learned to accept the rats.

Sherlock looked suspiciously at Harry Price, who held his hands up in protest. "Don't look at me," he said. "I've been beside you the whole time. You can't blame this on me!"

"That sounded quite defensive. Nobody has accused you," Sherlock said. Then he took a deep breath and scruffed up his hair. "Well," he conceded, "there's nobody here, and we don't have enough light to search the house until morning."

"So what do we do?" John asked.

"What we always intended," Sherlock replied. "We sit and we listen. I think it would be better if we split up, though, at opposite ends of the floor. John, Lestrade, you two take one of the bedrooms at that end of the corridor..." He pointed down the passage. "Mr. Price, I think you and I should team up for tonight. I'd like to keep an eye on you."

"Master bedroom," John said suddenly.

Sherlock frowned. "What?"

"You two take the master bedroom. It's on this side of the house, and it's the only one I've seen with an actual bed in it," John said. "Don't make me nag you, Sherlock."

"So. My German-speaking, American sister."

Harry Price, fiddling with a small digital recorder in the corner of the master bedroom, he looked up. Sherlock had been sitting upright and diligent on the mattress of the king-sized bed, but had eventually given in and was now sprawled out on the mattress like a tiger in the sun.

"I'm sorry?" Price said innocently.

"My sister. How did you know about her?"

Price looked confused for a second. "Oh," he said at last. "You know how, Mr. Holmes."

"No, try again," Sherlock said. "You researched me. And given my father's previous line of work, you went to a lot of trouble with it. I'm only going to ask you the following question once, Mr. Price. Why?"

Price was silent for a few seconds. "You can say it all you like," he said finally. "But I didn't research you, Mr. Holmes. I know almost nothing about you. And I've got no reason to lie about that."

Sherlock scoffed and sat up awkwardly. He'd taken his much-hated pills an hour before, and was a little light-headed for it. "You've plenty of reasons to lie," he said. "You make money out of telling people lies."

Price smiled. "You're quite right about the show," he said. "We use actors, plant spies among the real members of the audience... you name it. Are you really so shocked about that? It's television. People watch to be entertained. Psychic phenomena can't be produced on cue, that's the problem with it. And nobody's going to want to watch a show where nothing happens, so we help it along. But to say that this makes everything fraudulent... well, that makes about as much sense to me as claiming that the existence of a hundred servants proves that there is no master."

Sherlock turned his head toward him, but said nothing.

"I've got genuine abilities," Price said. "I've had them since I was a kid. When I was two, I told my mother all about the house she grew up in as a kid. They moved to the other side of England before she was married, and I'd never seen a photograph of it. How do you explain that?"

"I doubt you remember this," Sherlock said, uncomfortably reflecting on memories of his own from early childhood. "You have only your mother's word for it that this even happened. And even then, I imagine confirmation bias comes into it. You said what she wanted you to say about the house. She believed in your abilities, didn't she?"

"Does," Price corrected him. "She's eighty-four, but still kicking. And of course she does. You don't see a person prove over and over again that these things are real and still deny it. Wouldn't you agree that that would be an example of confirmation bias?"

Sherlock grunted and rolled back over carefully, looking up at the dim outlines of the threadbare bed-canopy above.

"So, Mel...?"

"Shut it, John," Lestrade said crossly from where he was curled up on the floor, trying to doze with only a sleeping bag for a mattress. He'd just decided that this was in some ways worse than camping – grass was softer than floorboards. "I don't know yet."

"Why're you dragging your feet?" John asked. "No, I mean, why really. 'Cause Molly says Mel isn't buying that whole 'kids' thing, and I'm not sure I'm buying it either."

Lestrade shifted feverishly, trying to find a more comfortable position. Across the room from him, John was sprawled out on his sleeping-bag mattress, as content as if it were a king-sized bed in the Ritz penthouse.

"I really buggered things up with Julie," he finally said.

"She's the one who had an affair or three."

"Is she?"

There was silence for a few seconds. "Jesus, really?" John finally blurted out. "Who was it, Donovan?"

Lestrade groaned and rolled over again. "All because Donovan was giving it to Anderson doesn't mean she was giving it to everyone," he said. "No, it wasn't Donovan. It was Lucy Parnell, if you really have to know."

"Parnell? Gregson's sergeant?"

"Yeah. She used to be my constable, until all that happened. Oh, I mean, nothing happened. It was only two or three times, and she didn't get all stupid about it and want me to leave Julie and the kids for her. It got awkward, that's all. I suggested she apply to change teams. Donovan got transferred across to me."

"Did Julie know?"

"Not that she's ever said. Like I said, it was over and done in a week. But that was before she started sleeping with Mark, so..." He trailed off.

"Okay," John said. "But that would have been years ago, right? Donovan's always been your partner, as long as I've known you."

"Going on nearly ten years ago."

"So what, you're worried you won't be able to keep the cue in the rack? If you haven't been cheating on Mel before now, I dunno why you'd want to start just because you put a ring on her finger."

"I've also got it on good authority that I'm a complete arse to be married to."

"Yeah, well, that's why you don't go to your exes for a character reference."

Lestrade sat up, yanked at the sleeping bag, and flopped back down again. "Could be wrong here, but I think I told you to shut it about five minutes ago."

"Fine." John yawned and paused, listening to the servant's bells clinking gently in the dark house. In the roof above, something made a heavy swooping noise, and then a squeak. Owls, of course. They always made such freakish noises when they were hunting... and hopefully, they were going to take care of the rats.

Lestrade lay tossing and turning for what seemed like hours after John had started to gently snore.

"Greg..." John shook him hard, then shoved him. With a reluctant groan, Lestrade stirred and opened his eyes.

"Wossisit?" he mumbled.

"Greg, get up, I need a bloody witness for this!"

At the word witness, Lestrade opened his eyes properly and sat bolt upright. Few things had caused more trouble for his career than an unreliable or non-existent witness. John had scrabbled to his feet and was now standing at the window, a lit candle and candle-holder in his hand, beckoning him over.

"What?"

"Hurry up!" John hissed.

Lestrade got to his feet with a little difficulty, joining him at the window and looking out. It was the early hours of the morning and still dark; on the horizon only a light or two from a farmhouse twinkled. The garden below sat in silent repose, the close-mown grass giving onto an inky smear of trees that bordered the property. Away to the right and down the slope was the skeleton of the old summerhouse, where Reverend Bull had dozed away his last days; but neither John nor Lestrade were looking at the summerhouse. Near the border of trees, something pale was moving.

"Oh, bollocks," Lestrade said under his breath. "I'll never say it. I'll never say I saw it..."

Only a woman could have walked with that kind of slow grace. She was slender and tall, her garments falling in bright, pale billows. There was a pearly luminescence about her, from the cloth covering her head to the tips of her skirt that trailed like moonbeams over the dark grass. Her face was turned away from the house, but even so, she seemed young and beautiful.

John turned, the candle still in his hands, and reached for the door. "Come on," he muttered, not waiting to see if Lestrade was keeping up as he rushed down the landing and the stairs as fast as he could in the near-darkness.

Trying to find the back door was harder than expected, especially in the dark; by the time John had located it, Lestrade was on his heels. The door was unlocked, but stiff and reluctant to open, even against John's shoulder. After a few jolts, it gave way suddenly, and they both spilled out into the chilly rectory garden.

She was still there.

Still maybe fifty yards off, and taking no notice at all of the arrival of two loud strangers. She had her back to them both and was picking her way across the grass toward the line of trees, both arms hanging simply by her sides. In the few breathless seconds that followed, both John and Lestrade noticed that her bare feet made no sound on the grass beneath them.

"Do something," John said through his teeth.

"Do what?"

"I don't know, talk to her or something!"

"Why me?"

"Because you're the police -"

"What do you expect me to do, then – arrest her for being a ghost?"

John rolled his eyes. "God, fine," he hissed.

He had taken three or four hesitant steps toward the apparition when, upstairs, a thud and a hoarse male cry broke the silence.

John turned on his heel and tore back inside, with Lestrade following behind. He took the stairs two at a time, fumbling along counting doors in the corridor until he burst into the master bedroom without knocking. In the weak halo of the candle he held and the one sitting on Price's suitcase in the opposite corner, he found Sherlock sitting on the floor. He was breathing hard, supporting himself on his palms. Price, fully dressed except for his jacket and shoes, stood beside him.

"What the hell happened?" John demanded, dropping to his knees beside Sherlock.

"I don't know," Sherlock muttered.

"You what?"

"I don't know!" he exclaimed. "We were standing at the window..."

John glanced over his shoulder at Lestrade. "You saw the nun, too?"

"We were standing at the window," Sherlock repeated staunchly. "Something grabbed me by the arm and threw me backwards onto the floor... oh, for God's sake, it wasn't Harry. He was beside me at the time, and couldn't have pulled at me like that."

"Can you get up?" John asked.

"Um. Maybe."

"Mr. Price," John said as he helped Sherlock to his feet, "you might have heard that Sherlock broke his back last Christmas. So if I find out you've been -"

Sherlock cut him off with a cry.

"That hurt?"

"No, I make these noises for fun sometimes," Sherlock snapped at him, reaching out to take hold of one of the bed posts.

John looked at him carefully for a few moments, as if weighing something up. "I'm going to the car for my case," he finally said. "Greg, gimme the keys."

"You're going to the car for what?" Sherlock repeated as Lestrade took the candle out of his hands and went back along the corridor to the bedroom they'd been sleeping in.

"I'm giving you a cortisone injection."

"Oh, for God's sake – "

"You'll take the cortisone, Sherlock, or we're going back to London. Tonight."

"I'd like to see you make me." Sherlock's pupils narrowed with vim. But John smiled.

"Oh, I won't need to," he said. "I'll just ring Mycroft now, at..." He checked his watch. "At half-past two in the morning, and tell him you've been thrown onto the floor and done your back in. I'm pretty sure he could make you."

"You wouldn't dare," Sherlock seethed, sitting down gingerly on the mattress just as Lestrade returned and put the car keys and candle in John's hands.

"You sure you want to go out there on your own?" he asked him. But John rolled his eyes.

"There's no such thing as a ghost nun."

"But we saw – "

"We really didn't. Don't move, Sherlock."

As he hurried along the gravel front walk toward where the car was parked, listening to the sound of the gravel under his shoes, John cast a glance or two around the side of the building where they'd last seen the ghostly figure. Once he thought he caught a glimpse of silver from amid the trees lining the property, but there was no time to speculate. He opened the car boot with a clunk, grateful for the familiar sound and the beam of orange light it spilled onto the inside contents.

Most of their luggage had been taken inside already, but there were a few items here and there that they hadn't yet bothered with. As he lifted his case out, something caught John's attention – a soft glisten of hard metal showing through the gap in a half-open, green hessian travel-bag. It looked almost like...

He frowned, reached over to pull it out, and found himself holding a high-powered Beretta pistol.