A/N: I am so sorry for the delay between updates! I have been very busy lately, with school and other commitments and stories. So from now on, I will be aiming to publish one chapter for this every fortnight. For people following my other story, 'Alternate Universe', the update for that will be up next week, and every fortnight after that.

As always, thank you so much for reading this story, and any feedback/advice/criticism is always appreciated! Happy reading!

Sherlock found himself in a room he recognised as his living room. The curtain-less windows seemed to absorb what little light was in the room, swallowing the effects of the pitiful light from Sherlock's candle when he moved close to them.

The room was completely devoid of furniture, the walls bare and the floorboards rough and broken. Nonetheless, Sherlock carefully moved all around the room, using his candle to peer into every corner. He even stuck his head inside the fireplace, peering up into the chimney in case there was a clue hidden there. He was rewarded for his efforts by a pile of soot falling onto his face.

Sherlock came out of the fireplace coughing, and decided to give up on the living room, moving on to a bedroom which would later become his and John's kitchen. That, too, was empty of both furniture and of clues. There were no windows in the small bedroom, leading him to wonder how people saw in the room before the invention of lights. He suspected that they would have done so with great difficulty, as he was doing now.

Deciding to dismiss the room, Sherlock cautiously entered the dull bathroom, which smelled damp and patches on the walls that felt suspiciously furry. He shuddered and hurried on to what would be his bedroom, which had a window leading onto an alleyway the again swallowed the candle-light.

At first, the room seemed to provide no answers, but as Sherlock was searching he became slowly aware of a low buzzing noise. Frowning, he stopped and concentrated hard for a few moments, finally recognising the sound as that of the sonic screwdriver that John had made. However, it sounded too close to be coming from downstairs where John was. Closing his eyes (not that it made much difference), Sherlock concentrated on locating the source of the buzzing, which he identified as coming from a floorboard under the window pane.

Sherlock ran the couple of steps towards the window, carefully placing the candle on the floor next to him. His fingers scrabbled around on the ground for a few moments, searching for the edges of the floorboard. He gave a small smile when he managed to grasp the edge with his fingernails, and slowly, carefully, he lifted the floorboard, moving the candle to reveal what lay underneath.

He was greeted by the sight of an instrument that he could only guess was a sonic screwdriver. It was similar to the one John had cobbled together earlier, it looked more refined and complete, and the light on the end was blue rather than red. A small piece of duct tape had been fixed over the button to keep the screwdriver turned on, so the tip was lit up and buzzing.

Sherlock analysed the situation. Someone had obviously placed the screwdriver there with the intention that it was found; but why? Was it another clue? How had the mysterious Doctor managed to hide it there? And why was he going to the trouble to set a treasure trail for his children instead of giving them the information directly? The screwdriver raised more questions than it did answers.

Suddenly, there was a knock on the door. Sherlock jumped and spun around, raising himself into a half-crouching position. He grabbed the screwdriver for good measure.

A candle appeared around the door, and Harry's face followed, disembodied in the darkness. "Find anything?" she asked cheerfully.

Sherlock's shoulders relaxed, and he stood up, taking his candle with him. "Just this," he said, raising the sonic screwdriver so she could see it.

Harry gasped, and crossed the room in two steps, taking the screwdriver from him and inspecting it. "Where was it?" she breathed.

"Under a floorboard," he explained, pointing downwards to where he had found the clue.

Harry crouched down and felt around, then came up with a frown. "Nothing there," she said. "No note, no address, nothing. Nothing to tell us what to do next. But what the hell happened to you?" she asked, noticing for the first time Sherlock's blackened face.

He rubbed a hand over his soot-covered face. "Oh, I forgot. I had an accident with the chimney," he told her, somewhat sheepishly.

She chuckled and shook her head. "I don't know," she said. "We leave you alone for five minutes, and you end up looking like you're auditioning for Mary Poppins."

Sherlock rolled his eyes, then moved backwards as Harry raised her hand to his face. "It's okay," she reassured him, and he moved back to allow her access to his face. She carefully used her sleeve to wipe at the soot around his eyes and mouth, then moved on to the rest of his face. Sherlock's eyes tracked her hands' progress, but other than that he was motionless.

After a few moments, Harry raised her candle to inspect her handiwork. "You'll pass," she said, "for now. We can get you cleaned up back at the TARDIS. But we need to show John this," she said, holding up the sonic screwdriver.

They both turned towards the door, stopping and jumping slightly when they saw the candlelight in the doorway, illuminating John's form as he leaned against the door frame. "You two all right there?" he asked dryly.

Harry felt guilty, but of what, she was not sure. "Sherlock found this," she said, crossing the room and handing him the still-buzzing screwdriver.

John's whole manner changed. He carefully inspected every inch of the screwdriver by the light of his candle, eyes wide and attentive. Then he slowly raised his face to look at Sherlock. "Where did you find this?" he demanded, brandishing the screwdriver.

"Under a floorboard, by the window," Sherlock told him.

"There's nothing else there," Harry interjected, "I checked."

Carefully, John pulled off the duct tape that covered the screwdriver's button. The buzzing stopped abruptly, and the room was overtaken by the sudden sound of silence.

"Well," John said finally, "I think we should head back to the TARDIS."

-o0o-

When they returned to the alley, a thin grey cat was nosing around the TARDIS, sniffing the base and rubbing up against the corners. When it saw them coming, it disappeared around the corner, its tail swishing out of sight as they reached the blue door.

John unlocked the door and led the way inside. Unnoticed by anyone, the cat slipped inside just as the door swung shut behind Sherlock, hidden from view by the stolen cape.

"So what now?" Sherlock asked as he crossed the metal bridge to the console. "Is there a method of scanning the sonic screwdriver to find your father?" He was surprised at how naturally the words rolled off his tongue.

John was frowning at a readout from the console, so Harry answered for him. "Not unless Dad has managed to put a dormant code somewhere in the software, which wouldn't affect the screwdriver but could give us a message. But that's unlikely, because it would take centuries of-"

John interrupted her mid-sentence. "Did anyone bring a cat in here?"

Sherlock shared a perplexed look with Harry. "A cat?" he inquired.

"Yeah, the TARDIS says there's one lurking somewhere in this room."

As if on cue, a small grey head appeared in one of the coral struts behind John, closely followed by the rest of the cat's body as it jumped fluidly onto a branch. Sherlock noticed the motion, and nodded his head towards the cat. "You mean that one there?"

John jumped and span around, staring wildly at the cat. He advanced upon it slowly, stretching one arm out in front of him. When he reached the cat, he carefully held out one finger and poked it gently in the side. It mewled softly at him, and he jumped backwards.

Sherlock felt a hand on his arm. "That's not…normal behaviour, is it?" Harry asked him quietly.

"Not as far as I can tell," he whispered back, "although to be fair, I am not exactly an expert on normal."

"You're not the only one," she reminded him, before striding over to John and tapping him on the shoulder. "What's up with you?"

He turned to look at her slowly. "The TARDIS let in a cat," he said. "It shouldn't let in anything apart from us."

"It let Sherlock in," she pointed out.

"Oh, he doesn't count," John said dismissively. Then he glanced at Sherlock, and elaborated apologetically. "I mean, the TARDIS didn't recognise his presence, because he was an anomaly. Now she's used to him, she can let him in and out and know there isn't a security breach. But that doesn't explain why she would let in a strange cat."

"The cat was in the alleyway for hours," Sherlock said. "Maybe they got to know each other in that time?" he suggested.

"That would be ridiculous," John told him. "The TARDIS is a machine."

"You said that she was a living matrix inside a machine," Sherlock reminded him. "It seems less ridiculous than some of the things that have occurred today."

"But she can't talk to animals, that's absurd!"

"Nevertheless," Harry interjected, "we should put the cat outside until we've figured out what's going on. There could be a security malfunction of some sort, so it didn't realise the cat was coming in until it was already here. Next time, it could be a dalek."

"All right," John said. He approached the cat again and held out his arms, gently picking it up. He stroked it under the chin while he walked over to the door, and it purred contentedly.

When John reached the door, however, the cat didn't seem to want to go outside. It clung to John's jacket with his coat, resisting being forced back out into the cold night. In the end Harry and Sherlock both had to help extricate John from the cat's grasp, and together they forced the cat out of the TARDIS.

Sherlock tried not to laugh at the situation. Three grown adults, trying to throw a cat out of a blue box. Harry, however, seemed strangely resigned, as if this was a regular occurrence.

John straightened his jacket and cleared his throat, striding back to the console. "Right. Now, we just need to check the whole TARDIS' security system for breaches or anomalies, and scan the entire software of Dad's sonic screwdriver. Piece of cake."

Famous last words.

As soon as John plugged the screwdriver into the computer, Gallifreyan words flashed up in red on the monitor. Sherlock guessed they were error messages from the way John scowled and became impatient. "What does it say?" he inquired.

"It says that the software is unavailable for scanning," John said with a look of irritation. "It's been corrupted somehow. It can be turned on, but it wasn't do anything, even open a door."

"It takes very advanced technology to corrupt a Gallifreyan sonic device," Harry said, frowning. "And there's only two races in the universe who can corrupt the technology like that."

"Let me guess," Sherlock said. "Time Lord and Dalek?"

"Got it in one." John said grimly, unplugging the screwdriver and turning it over in his palm. "Surely Dad would never do that to his screwdriver, it's too valuable to him. That leaves one conclusion."

"The Daleks got to it," Harry finished for him.

"But why would the Daleks leave a series of clues leading to your father's sonic screwdriver?" Sherlock mused. "Unless it was to trap you, of course, but there wasn't anything at 221B."

"Why would Dad leave us a series of clues?" John countered, holding up the screwdriver. "There are outside forces at work here, I'm sure of it." He lobbed the sonic screwdriver carefully over to Sherlock, who caught it easily.

"From what I've seen, it seems as if the Daleks are living beings rather than robots, and advanced ones at that," Sherlock stated. "Would they have the imagination to lave such a trail? Furthermore, would anybody else be able to use Dalek technology without their permission?"

John shook his head, picking up a cloth from the console and chucked it to Sherlock. "You've still got soot on your face," he told him. "The Daleks aren't at all lacking in the imagination department. And Dalek ships are notoriously difficult to crack. In school, we learned that there are three things in the Universe you shouldn't try to do, and number one was hacking a Dalek ship."

"What were the others?" Sherlock asked, wiping his face carefully.

"The second thing you shouldn't do is tell anybody what the third thing is," John said with a grin.

Sherlock raised his eyebrows, and was about to fire back a retort when Harry suddenly spoke up. "Could it have been Doyle?"

John blinked and looked at his sister. "Could what have been Doyle? The treasure trail?"

She nodded. "If I remember correctly from last time I met him, he was a good actor, or at least a good liar. He could have been pretending not to know anything. I mean, he had Wiggins out keeping an eye on us."

John frowned, and Sherlock pursed his lips in thought. "That could be true," John admitted, "but if so, why send us to the screwdriver? Would he be in cahoots with the Daleks?"

"Or with your father," Sherlock muttered, but neither Time Lord heard him.

"That would make sense," Harry was saying excitedly. "They could have engineered things so that the Sherlock Holmes books never existed. But the world needed a Sherlock Holmes, so one was created." She gestured towards Sherlock.

"And they kidnapped Dad," John continued, "and hid him somewhere on their ship, in the hope that we would go and save him!"

"There were no signs of life on the ship when you scanned it," Sherlock reminded him, placing the cloth he was holding back on the console.

"I've been thinking about that. There were no signs of life showing, yet there were Daleks on the ship as well. The detection software was definitely not faulty, so the Daleks must have created a room or something which wasn't detectable by their software. They tripped their own software, the bastards."

"The Dalek that Harry killed didn't know where your father was," Sherlock pointed out. "It said his last known location was the destruction of some cult."

"The Cult of Skaro," Harry confirmed. "But the thing about Daleks, Sherlock, is that they have no emotions apart from hatred. They are lying, scheming, balls of pure evil, and that's on a good day. There is no such thing as a good Dalek, or even an honest Dalek. If one was threatened, it would rather die than be honest."

"You believed it," Sherlock stated.

"We were confused and scared!" John said. "Look, why are you so disbelieving? This theory makes complete sense!"

"Except," Sherlock said, "for why the Daleks would go to the trouble to erase a fictional character just to get their enemies to find a screwdriver, which would tell them that their father had been captured! Wouldn't it be simpler just to kill you and be done with it?"

"Like John said, the Daleks are not lacking in imagination," Harry pointed out. "If they wanted to kill us, which they do, they would prefer to make us run into their trap and then kill us."

"So your father may be dead already," Sherlock retorted, slipping his hand into his pocket.

"True," John admitted. "But there's a possibility he's still alive, don't you see? We have to take this chance, no matter how slim it is."

"You're walking into what may well be a trap," Sherlock said, "on the off-chance that you can save your father without being killed yourselves, all before analysing the situation and looking at all the facts."

"What other facts are there to look at?" John demanded.

Harry walked over to Sherlock, noticeably calmer than her brother. He turned to her, and she placed a serious hand on his shoulder. "It's okay if you don't want to do this, Sherlock," she told him solemnly. "We can use the TARDIS to take you home right now. You can forget all of this: time travel, space, everything. No Daleks, no kamikaze rescue missions. Just Earth and detective cases and normalcy. Nobody will think any worse of you for choosing that option."

Sherlock narrowed his eyes at her, a movement so slight it was almost unnoticeable. "Are you trying to put me off?"

"God, no," John said from behind Sherlock. He turned, and John offered him a crooked half-smile. "Trying to recruit you."