Judging from the look on PC Jack Neil's face as he trudged back up from the end of the street, his enquiries as to whether there were any witnesses to the murder of Mary Ann Nichols had come up with bugger-all.

"There are two security guards down at the Sports Centre," he told Lestrade. "And then two more at a couple of factories up toward the railway line. None of them said they heard or saw anything suspicious. If you ask me, though, the bloke on security at Brown and Eagles' wouldn't have noticed if I'd punched him in the face."

"You should've," Lestrade said sourly. "It might've helped jog his memory." By East End standards, Buck's Row had been quiet and still when the first responders arrived. But it was still a city street, and there were people living and working close by. Lestrade had sent PCs Neil, Thain and Mizen in opposite directions to make enquiries, and each of them had come back with nothing to report. Nobody had seen anything. Nobody had heard anything.

And if Lestrade had been inclined to mistrust the officers at Bishopsgate, his own crew had backed this up. Why Sherlock had insisted on going back with Dyer and John to interview Fiona Green was a mystery to him; she'd already told Dyer she had no useful information. Almost directly across the street was another flat, one tenanted by a Walter Purkiss and his wife. Purkiss, a grubby, middle-aged man with appalling bad breath, had told Lestrade in person that he hadn't heard or seen anything. Neither had his wife, even though she was sick with gastro and had been up and down from her bed all night.

"What I don't understand, sir," PC Neil said, taking off his cap momentarily to shake the rain off it, "is how come I didn't see anything. I mean, that's the whole point of being on the beat, yeah?"

"Yeah," Lestrade said, unimpressed. "You didn't have a partner with you?" It had been a while since he'd been in uniform, but he distinctly remembered the old rule that officers were not allowed to wander about in uniform on their own, especially in dodgy areas.

Neil laughed, though he didn't sound amused. He was a big, barrel-chested young man with a ruddy face and a no-nonsense attitude; he struck Lestrade as the sort of person who was brought up the eldest of fourteen siblings. "Budget cuts," he explained.

"Great."

"You're telling me. One officer on his beat, armed with a glorified stick, isn't going to scare a roving gang, now, are they?"

"You didn't see any roving gangs tonight, though."

Neil shook his head. "Not tonight," he said, in tones that implied this had made for an unusual shift. "But this beat never took me far from here, sir. Just through Whitechapel Road and up Baker's Row." He pointed in that direction. "I started at two, and I've been up this street every fifteen minutes since… he's a quick bugger, then, with nerves of steel." He paused, fumbling, as if unsure of how to put his thoughts respectfully. "Might she have been killed somewhere else and dumped, sir? Didn't look like much blood to me, and that'd explain why nobody heard anything. You'd barely notice a car driving down this way…"

Whatever he said next, Lestrade couldn't hear it. A train had just shunted its way along the railway line below them, and its roar cut across even Neil's sturdy Welsh baritone.

Lestrade stood deep in thought as he waited for the engine to pass. John could have been right about the strangulation, of course. Either that, or the killer might have taken advantage of the timing of the trains…

"Inspector Lestrade…?"

He turned to see Philip Anderson had just exited the evidence tent still surrounding the body, head to foot in scrubs. He decided not to tell him that Sherlock had been in the tent with no protective gear on at all, unless circumstances forced him to.

"Anderson." With an apologetic nod to Jack Neil, Lestrade dismissed him and went over to him. "Hey, look, both PC Neil and I have had the same thought seperately, so I thought it worth an ask: she wasn't killed elsewhere and dumped, was she?"

Anderson shook his head. "I can see why you'd think that, but it looks like most of the blood soaked into her clothes and pooled underneath her. And on that note, I've found something interesting—it's too hard to explain, so you'd better come and see what I mean..."

Once Dyer, Sherlock and John reached the footpath outside the flat of Fiona Green and her three children, it became obvious that one of the Green children was a baby. A very unhappy baby. The dishevelled, fortyish woman who answered to Dyer's knock looked close to passing out from exhaustion, though behind her the hall floor was waxed to a blinding sheen and they caught a glimpse of an upmarket kitchen, all shining chrome and glass. A working professional, Sherlock immediately decided. One who was paid well and had a generous maternity leave entitlement that had run out in the last week or two. Despite the appalling hour, all three of her children were up and active. A small girl of four or five stood open-mouthed in the far doorway, staring shyly at them through a thick fringe of dark brown hair. Obviously an inheritance from her father, though her pointed chin and huge green eyes were uncannily like her mother's. A small boy, perhaps two years old, scampered across the hall wearing a pair of rompers. The miserable baby was in Fiona's arms. He was a dull child, with a head so bald he seemed to not have any hair at all, wingnut ears, and eyes that were deep-set and too close together. Sherlock thought of tiny Sophie, with her delicate Hooper features, damp dark hair and butterfly eyelashes.

"We're so sorry to disturb you again," Dyer was saying.

"Oh, you could hardly disturb us any more than Max is," Fiona said wearily, brushing a frizzled lock of dyed blonde hair off her forehead with one hand. Baby Max was flushed and restless in her arms, and abruptly went into a fit of bark-like coughing.

"That sounds like croup," John said. Then, seeing Fiona's expression, "Oh, um. Hi. John Watson," he said, holding his hand out for Fiona to shake. "I'm actually a doctor. I'm here with the detectives because… actually, yeah, never mind that. Can I ask, how old is Max?"

"Thirteen weeks."

John nodded. "Immunised?"

"Of course," she said.

"You'd be surprised how often I hear 'no'," John said. "I don't think it's whooping cough, but I thought I'd do my best to rule it out anyway."

"Do you know, Dr. Watson," Sherlock said amiably, steering John toward the staircase that led up to the second level of the flat. "You and Mrs. Green should take the baby upstairs so you can talk about this in privacy."

"Sherlock," John protested. "We haven't even—"

"Hippocratic oath, do no harm, you know—"

John glanced at Fiona. Behave, he mouthed to Sherlock, when he was sure she wasn't watching.

"Always," Sherlock replied audibly, then, realising he'd forgotten to, he also held out one hand for Fiona to shake. "Ms. Green? Sherlock Holmes, consulting detective for the Metropolitan Police," he said briskly. "Detective Constable Dyer and I would be delighted to keep an eye on your older children while Dr. Watson has a look at little… er… Max."

Reluctantly, John followed Fiona up the narrow staircase. Sherlock turned back to the hall where Dyer was still standing, looking a little bewildered at what had just transpired.

"Sherlock," he whispered, folding his arms. "You know we can't interview the kids. It's illegal. And even if it wasn't, these two are both way too young to take their evidence into—"

"I'm not a lawyer," Sherlock said. "If we find Polly's killer, I don't care how we got there legally."

Dyer sighed. "You seriously think kids in nursery school can help us anyway?"

"Perhaps. You'd be surprised at what they notice. More importantly, young children don't make up justifications for things they can't explain…"

The girl had just padded into the hall in her bare feet, full of curiosity. She circled Sherlock carefully once or twice before pulling at his sleeve and announcing, "Excuse me. I'm four!"

Automatically, Sherlock found himself reaching for one of Lestrade's insufferable Dad-jokes; one he'd used when a seven-year-old witness had made a similar declaration out of the blue the year before. "Hi, Four," he said. "I'm Sherlock."

She giggled. "No!" she said. "I'm Emily! I'm four, I just had my birthday."

"Oh," he said. "… Happy birthday."

"We had cake."

"Did you?" More of Lestrade's kid-side manner.

"Chocolate cake."

"… I like chocolate cake too." Was that the right thing to say? He couldn't see anything controversial about it. Apparently, Dyer didn't feel he needed further handling. Sherlock watched him go down the hall and into the room where the boy had just disappeared.

"You look sad," Emily said, peering up at Sherlock. "Why are you sad?"

This was decidedly more dangerous than discussing the merits of chocolate cake and birthdays, especially given her age. "Because," he said, "a lady got hurt outside, a little while ago."

"Oh." Her brow furrowed. "Did she fall over?"

"Maybe. We think someone might have pushed her over on purpose." Sherlock knelt down to Emily's level. "Did you hear anything from outside a little while ago?" he asked her. "Maybe you heard the lady crying, or someone being mean to her…?"

Emily considered this, then shook her head. "Nope," she said brightly. "All I could hear was Max crying. He's been crying for aaaaaages..."

If Sherlock expected him to use a sick baby as an excuse to connive information out of Fiona Green, John thought vindictively as she handed baby Max over to him, then he had another thing coming. Nichols was dead, and no changing that. Max Green was alive, and John's priority was keeping him that way.

"Pretty miserable," was his final opinion, after examining the baby as best he could without benefit of equipment like a stethoscope. "Mid-range fever. Is he teething yet?"

"Not that I can tell. Dean and Emily didn't teeth until about five months."

"Then all that drooling is a bit of a worry—he mightn't be able to swallow his own saliva properly, and that's a choking hazard…" Then, seeing her expression, he said, "I don't think it's worth your while rushing him to A&E. But he does need to see a doctor as soon as it's convenient—I can't examine him properly or prescribe anything right here and now. Listen, can you get him over to Shoreditch later this morning? Got a friend in private practice there who might be able to see you. Dr. Abato. He's good—I'd trust him with my own kids. We can give you a cab voucher if you're having trouble with transportation."

"Thank you," she said in some bewilderment, reaching out to take Max back. "That's very kind of you."

"Not often you get a house call these days," John agreed, adopting his usual professional mannerisms as he pulled his notepad and a pencil out of his pocket and scrawled out a note to Nicholas Abato, another old friend from Bart's. Taking advantage of the lull in conversation, he kept an ear out for the activity still going on in the street outside. But although the flashing lights were visible through the half-open window, he could hear nothing much except Max's grizzling noises and the other children downstairs… Was Sherlock interrogating a toddler down there?

"Now listen," he said in his most confidential way, handing the note over. "Like I say, I've got three kids, and I know what it's like to sit up all night with a sick baby. You didn't hear or see anything unusual from outside in the last, say, hour or two?"

"If you're a dad of three," Fiona said, putting one weary hand to her forehead, "then you'd know I didn't. All I was concentrating on was Max. I don't think I'd have noticed if World War Three had broken out in the street."