"What took me so long?" John repeated in equal parts fury and confusion. "Me? You left me and Molly I in a car two weeks ago, telling us you'd be along in an hour!"

"I was abducted and left inside a burning house."

"What?"

"Not entirely sure as to why, but I'm getting closer. Over the past weeks members of the Homeless Network collected intelligence on related crimes going back thirty years. Why haven't you turned on the lights?"

"You're the one that's been sitting in the dark, why haven't you?" John asked as he banged the lights on. "What have you done to my flat?"

All the walls and the windows were covered with news clippings, official police files, forensics photos, and scribbled notes.

"Your flat? This is our flat."

"No, you're dead. This is my flat. And where's Molly?"

"She's looking over something in my room."

"Her room, actually, which it will be until Sebastian Moran is put on trial."

"Ah. Forgot about him, more pressing matters, John."

"You can't just show up whenever you'd like after disappearing for weeks and expect that we'll drop everything to help you."

"My brother can be insufferable about covert operations," Sherlock replied, not really listening. "He assured me you had been contacted. Never mind. The case at hand must be dealt with immediately, It is the to figuring out The Engineer."

"The Engineer?" John repeated. "Sherlock, Sebastian Moran abducted us trying to find you. He's threatened both me and Molly - dunno if you care - and he's got the resources to do it. How about we put him away before we waste time on anything else?"

Still ignoring John, Sherlock pointed to the largest board. "This was the house I was trapped in. Five dead from gunshot wounds. One burned before the rest. Arson consumed most of the house, but I was able to place everything in my mind palace before it was destroyed."

"Okay, so what are these other cases, then?"

"They're nothing. Six cases, six! In the past fifty years, these six cases alone have some similarities to this most recent case. Worchester 1982. Curlew and Hobby confirmed the original investigation's conclusion as well as Hartlepool 1988. Osprey and Wagtail likewise confirmed the murders in Telford 1996."

"Who are these people? Wagtail and Hobby?"

"Do pay attention John! Members of the Homeless Network. Mycroft insisted on code names. For his imposition and your reference, his name is Blue Tit."

"What about me?"

"Pintail."

"And you?"

"Swift."

"And what about me?" Molly asked as she emerged from her room. "Do I have a code name as well?"

"Turnstone," Sherlock replied. He continued as if there had been no interruption. "Northampton 2010. Family annihilation followed by arson. The father, Jacob Quincy, assumed to be the perpetrator. Roller and Tern are currently correcting the record."

"An explosive fire?" Molly asked as she glanced over the board.

Sherlock continued in his bored voice. "Equipment failure produced excess carbon monoxide on the second floor. Faulty heaters started the fire on the ground floor. The carbon monoxide initially prevented fire from spreading to the top floor, but the eventual lack of oxygen created a vacuum, which dragged in the remaining air, pressurized the main floor, and caused an explosion. All very basic and very boring."

John said, "What you're saying is this house had a carbon monoxide leak and a devastating fire, both from separate, faulty equipment that failed on the same night, and I'm guessing there must've been a defective alarm system as well. So are these the unluckiest people on the planet, or was someone trying to kill them?"

"Reasonable conclusions," Sherlock said, sounding surprised. "But incorrect. The Quincy family let the house, and the facilities management of the rental company certified everything weeks before; thus the assumption that the father orchestrated everything. But with limited inquiry it became obvious that maintenance saved a considerable amount over several decades by falsifying certifications and reports, checking requirements once every three years rather than each year or every six months. Roller and Tern agreed to set the record straight."

"Someone named Roller figured this out?" John asked.

"No, don't be ridiculous. My deductions solved this case, but to maintain my death, others had to handle the day to day and physical elements."

John vividly remembered Sherlock forcing him to wear a wire and a camera during an investigation.

"All a waste of time!" Sherlock continued. "Killdeer and Puffin are keeping me appraised of the extradition of the Bridgewater killer, while Waxwing, Rook, and Shrike are all handling the polygamist framing in Ashford. Two weeks squandered correcting blunders so obvious a review panel could have identified them. No closer to The Engineer."

Molly and John shared a look of confusion.

Molly went first and asked, "Bridgewater killer?"

"Bridgewater 1991. The Millard family found shot dead, save for one Rita Millard, eldest daughter, missing and presumed dead for the past twenty years. It only took a manner of minutes to confirm that Miss Millard was the killer and fled to Germany under a new identity, Diana Wimble, currently being extradited back to England."

"Polygamist framing?" John asked.

Sherlock sighed and replied, "Ashford 2007. The Hasting family was murdered, assumed to be murder-suicide by the father, Leo. The initial investigation missed the fact that Leo Hastings was a polygamist with at least one other family, consisting of Emily Hastings and her two children. Emily's father discovered that his son-in-law had another family and sought revenge. Spent almost an entire day on this case, nothing to show for it."

"Sounds to me like you're on fire," Molly said.

Sherlock's expression became confused, and John couldn't hold back his smile. It wasn't every day that someone put Sherlock Holmes off one of his rants.

She continued, "I mean, you solved three cases from the past thirty years and found a fugitive believed to be dead. All without exposing yourself. The last time you solved two cases in a row you said you were 'on fire.'"

"Ah, yes, well, then," Sherlock said awkwardly. "To be clear, I have spent two weeks of my skill and the real crime has gone unsolved."

Silence filled the room.

"Real crime?" John asked. "You mean the deaths of six families don't qualify as real crimes?"

"Awkward?" Sherlock asked.

"Yes, completely," Molly replied.

"These other cases were poorly investigated, but not one is the right crime," Sherlock said, annoyed he had to clarify.

"You do realize we've no idea what you're talking about," John said.

"Actually, I think I might," Molly said. "I autopsied five bodies, separately, over the past two weeks. I thought the reports were missing, but – "

"Mycroft arranged evaluations under an umbrella term," Sherlock replied. "Again, you're focusing on the wrong things. The Engineer put me in a burning house with five bodies. She's either recreating a crime, which doesn't seem to be the case, or wanted my attention on this crime."

"In the future, you should start with that," John replied. "And what's Dollhouse?"

"Mycroft classified the documents, or something like that," Molly said. "He controls the only copies. Investigations like that are branded with a short hand."

"Yes, yes, what did you find?" Sherlock demanded.

"None of the five individuals I autopsied were related," Molly replied. "They all had false names assigned to them, but I ran DNA against the system anyway. And it explained all the inconsistencies I noted in the reports. None of them died of gunshot wounds, for example. The DNA tests came up because the bodies were donated to science. They were allocated to medical programs in Oxford."

"So these Dollhouse people weren't murdered?" John asked.

"No, but someone went out of their way to make it look that way," Molly replied. "I can tell that even though the post-mortem burns removed a lot of evidence."

"There was blood spatter," Sherlock said. "Before the house burned down, consistent with the trajectory of the gunshots."

"I can't confirm without blood samples, but it's possible someone else's blood was used to replicate the patterns of living bodies."

"Why?" John asked. "If the house was burned down on purpose, why bother with forensics that would burn up?"

"Because she wanted me to see it," Sherlock said. "I reviewed all the cases even close to resembling the crime, going back fifty years, and none of them match. Not one replicates the scenario of the fire. None of them has a victim killed at least fourteen hours before and burned at the scene."

"I think we need some tea," Molly suggested.

The next morning... The pounding just wouldn't stop. At first, John thought it was a headache, but after it continued for several minutes, he realized someone was beating down the door. He got out of bed and donned his robe.

The knocking continued relentlessly.

"All right, all right!" he yelled as he came out of his room.

Molly's door popped open, and she asked, "John, who is that? Oi, where is everything?"

As of four hours ago, Sherlock Holmes had filled the living room of the flat with boards, case files, and equipment for various experiments, yet now it was completely empty, as if the consulting detective had been nothing more than a shared hallucination between John and Molly.

"Where's Sherlock?" he asked.

"Dunno."

The increased volume of the knocking drew John to the door. No sooner had he opened it than Lestrade pushed past him.

"Where the hell have you been?" Lestrade demanded. "I've been at your door for fifteen minutes!"

With that, he marched up the stairs.

"Molly, good you're not dead."

"Why should I be?" she asked.

"For one thing, I've been outside making enough noise raise every neighbor on the bloody street!"

"Why didn't you call?" Molly asked.

"What are you on about? I did call. I've been calling for nearly thirty minutes. Neither of you picked up, not even Mrs. Hudson. Then here I am, outside your bloody door, and here you are, completely unawares. I've got to ask, am I interrupting?"

"Interrupting what?" John asked.

She said, "Never mind that, why are you here at half past five?"

"I'm here to take you two into protective custody."

Philip Anderson had worked horrific crime scenes, but this one was particularly shocking. Two bodies dumped right in the open outside the Broadway Post Office along Caxton Street.

"Right in our backyards, eh?" Sally Donovan commented.

"I'd say," he replied. "They weren't killed here. No blood spatter for one thing, and no signs of a struggle. We haven't done samples yet, but I did get fingerprints."

"I'll take a guess at cause of death. What do you reckon? A dozen gunshot wounds?"

Anderson nodded. "Six in the male victim. Seven in the female, who I'm fairly certain is Riley Wendell."

"Wendell. She's the one that was mixed up with Sebastian Moran, wasn't she?"

"Soon as I said that to Lestrade, he ran straight off," he replied. "Even though I mentioned we're still waiting on confirmation from prints."

"Looks enough like that photo we've been circulating for weeks," Donovan said.

"Can't really tell if the bloke is Gregory Wendell, not with his wounds. Have to wait on confirmation."

Both their mobiles rang with a text alert.

"You get this message about the killer being an assassin called The Baker?" Donovan asked. "That's got to be some kind of spam or something."

"I don't think it is. I sent in the crime scene photos to run through Interpol and our crimes database. Lestrade was certain this was a professional job."

"But, seriously, The Baker?"

"Named because every job he's done has used exactly thirteen bullets, a baker's dozen. Bit weird, isn't it? Thirteen bullets. On top of that, the killer only ever uses revolvers, which means he must reload three times to complete the hit."

"Seems like he uses two guns," Donovan suggested. "The ballistics reports from some of his other hits show he uses flat nose, thirty-eight caliber bullets, but forensics concluded they weren't all fired from the same gun."

"Then he'd still have to reload one of them, since six bullets is the max for most revolvers."

"Well, after you've shot a guy twelve times, you really think he's got a chance of escaping while you reload?" Donovan asked. "I knew this day would be no good, soon as I got out of bed. I've got a few to interview before I catch up with Lestrade. You'll call me with news?"

Anderson nodded.

Sherlock Holmes paced in the basement in 221 B, surrounded by the walls of evidence he moved from the upstairs flat the night before.

He couldn't remember properly, but he knew that he had spoken with The Engineer before he blacked out. Whatever she used to drug him made him forget two full days, and only bits and pieces of the conversation broke the silence.

It felt like I wasn't there. Like I had just dissipated into the shadows and the grass and dirt... just a symphony of rising lights vanishing into the moonlight.

That last bit was clear. It must have been the last thing she said to him before she left, but why did she tell him a story about sitting outside and watching fireflies? Wouldn't it have been more sensible to tell him about the crime that inspired the house fire she was about to set? She spoke to him, so it was logical to assume that he spoke to her, no matter how drug-addled he happened to be. What question did he ask to elicit a response about fireflies? And why hadn't Mycroft given him copies of the files on The Engineer? It had been weeks since he asked.

In need of distraction, Sherlock riffled through one of the boxes he brought down from the living room. A small notebook tumbled out. It looked like one of John's, but it was new. Why should he need a new notebook? Without Sherlock consulting on cases, surely John had no reason to take notes.

He scanned through several pages dedicated to the most mind-numbing crimes imaginable: petty theft, pickpockets, lover's quarrels leading to murder. Sherlock didn't recognize anything, which could only mean that John was solving crimes without him.

Boring crimes, of course, but crimes just the same.

The last page mentioned a broken bust, an insurance scam, and a man named Anthony Wilder. The citation suggested that the burglar tried to find something inside the broken statue, which was curious. Sherlock stared for a moment at the pictured taped to the page. He recognized it; in fact, he'd seen it quite recently.

The argument upstairs suddenly became much louder. Sherlock made for the door to demand silence, but before he could reach it, Mycroft burst in.

"Ah, little brother," he said, "time for a field trip."

"Donovan," she said as she answered her mobile.

"Where are you?" Lestrade asked.

"Was cleared for a trip to Woodhill Pirson. I rang several times and left messages... figured you'd be all tied up at Baker Street for the day."

"No, but it longer than I thought. Listen, be careful with Moran. He's all polite until he pays someone to kill you."

"If we had evidence to link him to the two bodies from this morning, I wouldn't be spending my afternoon at the Closed Supervision Centre, now would I?"

"Right, then, call me before you start back."

Mycroft convinced Lestrade that he could protect Molly and John at one of his secure facilities better than shoving them into a random safe house.

He then pilfered both their mobiles and loaded them into a car with Sherlock. It took three hours to reach the super-secret location, and when they left the car, they found themselves in an enclosed garage. Mycroft led them through a heavily locked door and into an enormous room. It had the makings of a large library: stacks of shelves filled with volumes bound with pinch shells or ringed binders, cabinets that clearly accommodated a complex filing system, and a very large area dedicated to what seemed to be museum pieces.

"Where are we?" John asked.

"An archive warehouse," Mycroft replied. "Containing reports, case files, data collection, and anything else we have ever tied to the individual known as The Engineer."

"Which section?" Molly asked.

"Section? No, my dear, this warehouse is dedicated to her exploits entirely."

Sherlock didn't find that comment surprising. "Only confirmed involvement?"

"Per your request, I've added a liberal amount of 'possible cases'," Mycroft replied. "Crimes and events she may have had a hand in, but you hardly provided adequate parameters. That, and by necessity, any cases that we've come across that bare similarities of any kind to her work are included here, even those that occurred before her time, as some individuals become inspired by historical affairs. Everything is clearly marked."

"Sorry, this entire place is, what, The Engineer museum?" John asked.

"So to speak," Mycroft replied.

Sherlock rushed off to some distant corner and disappeared behind the shelves.

"Why are we here?" Molly asked. "There're no bodies here for me to analyze."

"And contrary to popular assumption, I do have a life," John added.

Mycroft gave a small smirk. "Forgive me, but knowing my brother's propensity for obsession, I thought it best for him to have people around who can stand him."

"I'm not sure we qualify," John said.

"So we're here to babysit him?" Molly asked.

"Ensure that he's fed and clothed, or at least has trousers on. I doubt he'll sleep, so I won't hold you responsible for that. And I didn't lie to Lestrade, you are under strict protection here, you will be safe. I'll come collect you in a few days."

John considered the facility again. He said, "I've met this woman. She can't be more than thirty. There's no way this entire place is dedicated to her. Most criminal cases have a file I can fit in my hands."

"Erroneous assumptions!" Sherlock shouted from afar.

"Indeed," Mycroft said. "A case file is for investigators building a legal case against certain individuals. That model is affective for most crimes, but in situations involving more nuance, such as foreign and domestic allies, assets, spies, and other agents, we need a more... comprehensive system."

"Allies? Agents?" John asked. "Are you saying The Engineer worked for you at one point?"

"Goodness no," Mycroft replied. "Don't let the terminology fool you. They may be on our side or even in our employ, but that hardly makes them trustworthy in all scenarios. In fact, we can only rely on some assets when dealing with specific enemies. That's why complex and complete documentation is so important."

"So, errr, this woman, she's some kind of... frenemy?" Molly asked.

"Seems to me like she has her own agenda," John said. "Is that right, Mycroft?"

But he was gone.

Lestrade knew something was wrong when he couldn't get anyone on the line. He kept at his desk, trying to catch a lead on The Baker or at least discover where the Wendells fled before their deaths.

Then Donovan sent him a text.

FROM: Donovan
MESSAGE: Riot and fire at Woodhill. Signs of breakout.

He responded with his own text: "What do we know?"

FROM: Donovan
MESSAGE: Unconfirmed. 4 prisoners dead and 2 guards injured. 2 attempted escapees recovered. Head count still running.

Lestrade bit his lip before sending, "Moran?"

FROM: Donovan
MESSAGE: MIA. Possibly injured or dead.

He sat back at in his chair. Something told him that Moran wasn't the kind of man to die in a riot or a fire.