After a reflective half minute on the street outside, Harold finally spoke.

“Well,” he said, “the bad news: Whoever that guy was, with the goatee, he took everything of any use out of that apartment. No diary, okay, but not even a spare photocopy of the diary. Or any excerpts that Alex had typed up. Or notes on what was in it. Did you notice the laptop power cable beside the desk? Ten to one there used to be a laptop attached to it, and he took that, too. There were plenty of books on Conan Doyle, sure, but not a single piece of information about the diary itself, or how Alex had found it.”

“Is there any good news?” asked Sarah as they walked toward Argyll Road.

“Yeah. We’ve actually laid eyes on someone who’s mixed up in this, whatever the hell ‘this’ is. And we know the guy’s not a Sherlockian. Or at least not an Irregular; I’d have recognized him if he was.”

“I suppose that’s something like good news. But I think I can do you one better.” Sarah reached into her coat pocket and removed a thumbsize piece of purple plastic. She handed it to Harold. “A flash drive. It was in one of the drawers on Alex’s desk.”

“You stole it?”

Sarah just shrugged.

Harold was impressed. He could never tell whether she was two steps behind him or two steps ahead.

“Not sure if anything useful is on it, but we can check it out back at the hotel,” said Sarah, turning her head to look behind them once, and then again a few seconds later. “I have some bad news, too.”

“What?”

“I think we’re being followed.”

Harold felt his body grow suddenly tense. “Seriously?” he asked.

“I’m going to kneel down on one knee, as if I’m adjusting my shoe. When I do that, come in front of me and turn to face me, and talk to me as if you’re just naturally continuing our conversation. Then look casually behind us and see if you notice a big guy in a leather jacket. Ready? Go.”

Sarah dropped her right knee to the pavement, and, leaning over her left, she reached into her left shoe as if she were trying to remove a stone from it. She had on thin black flats, out of which she pulled her heel, running her fingers along the inside lining of the well-worn shoe.

Harold turned to face her, doing his best to seem casual. He placed his hands in his pockets as he spoke.

“Okay, this is me talking to you,” he said, “I’m still talking, blahblah-blah, here I am talking.” He gazed past her down the street. Among the throng of pedestrians-a hand-holding couple, a jogger in a tracksuit, an Indian family of four-Harold quickly made eye contact with a large man in a leather jacket and loose blue jeans. He was heavyset, with a circular head and puffy cheeks. The coat looked flimsy, and the man held his hands in his pockets to keep them from the cold.

Shit, thought Harold, realizing he’d just exchanged a glance with the man. Harold flicked his head abruptly to the right, finding a distant street sign at which to stare.

“We just looked right at each other,” he said. “I think he saw me notice him.”

“What’s he doing now?” asked Sarah as she continued to fiddle with her shoe.

Harold kept his face aimed at the street sign-”KENSINGTON PALACE,” it read, accompanied by a tiny picture of a walking man, and an arrow pointing behind Harold’s back-while he tried to turn only his eyes to the left, in order to spy on the man. The motion made his eyes hurt. The heavyset man had averted his gaze as well, and he seemed to be occupying himself by staring into the front windows of a tanning shop.

“He’s looking away,” said Harold. “Definitely seems fishy.”

Sarah placed her heel back in her shoe and stood up. She led Harold down Kensington Road with a quickened step.

“What should we do?” Harold finally asked.

Sarah raised her hand and stepped from the curb onto the street. “Get out of here,” she said.

A cab came quickly, and the two shuffled inside. It was only after they had shut the taxi’s door behind them and the driver had turned his head around to inquire about their destination that they both realized they weren’t sure what to say.

“Umm… not the hotel?” asked Harold.

“He might know where we’re staying already, but just in case, let’s not tell him.” Sarah raised her voice as she spoke to the driver. “Do you mind just heading straight for a minute while we figure out where we’re going?”

By way of response, the driver-a South Asian man with dark hair and a prodigious mustache-shrugged. He switched the car into Drive.

Harold and Sarah both swiveled in their seats and looked out the taxi’s rear window. The man in the leather coat was on his cell phone.

As they watched him recede into the distance, however, they saw a quickly moving black car come to a sudden stop in front of him. The man lowered his cell phone. He pulled open the car’s door and swung his wide frame inside the car in one continuous motion; it appeared surprisingly graceful for a man of his size. The car sped forward, growing larger in the taxi’s rear window. It was headed straight toward them.

Harold turned back to the driver. “Do you mind going a bit faster?” he said.

“Faster?” replied the driver. “Faster to where?”

“Wherever,” said Sarah. “Up that way. And faster.”

The driver shrugged again, and gave a knowing shake of his head. Americans!

Behind them the black car weaved between lanes, aggressively making up the distance between it and the taxi. The side windows of the black car were darkened, so Harold couldn’t make out who else might be inside. His view into the car’s front window was obstructed by one intermediate car, and then another, until finally he managed to get a second’s clear view of the black car’s driver: a balding young man in a gray sweater, who sported an awful goatee.

Harold inhaled sharply.

“Holy shit,” was all he managed to say.

Sarah saw the Goateed Man at the same time as Harold did. She turned instantly toward the driver.

“Hi,” she began, “would you please make a right turn up at that light? Yes, right here.”

“Missus,” the driver replied, “what is going on?”

“Please turn right here, now!” barked Sarah.

The driver switched lanes and took the turn.

“I do not want to be part of any trouble,” he said as they headed south past Imperial College.

“Neither do we. So let’s try to avoid trouble as much as we can, all right, by making a sharp left up ahead.”

“I will drop you off at this corner here.”

“No!” interjected Harold. “We’re being followed.”

“Come on, now,” said the driver. “Time to get out.”

“Sir, I’m being completely serious. Look at the black car behind us. They’ve been following us since we got into your cab.”

The driver looked up into his rearview mirror. There were more than a few black cars.

“Why would someone follow you? What, you are a famous actor or something?”

“Actually,” said Harold as he thought the matter over, “that’s a good question. I’m not sure why they’re following us As far as I can tell, they’re the ones who have something we want.”

“So maybe I pull over here and you can go to figure out who is chasing who.”

“That’s not a bad plan,” said Harold.

Sarah looked at him strangely. “What?” she asked hesitantly, as if she were afraid of the answer.

“I have an idea,” said Harold. He reached into his wallet and removed a tight clump of bills. Without checking to see how much money he was handing over, he folded the clump and handed it to the driver. The cabbie looked pleased as he thumbed through the money.

“I need you to do one more favor for us,” Harold continued. “Speed up. A lot. Then pull a quick left up ahead, at”-he squinted to make out the street sign-”Fulham. Then stop abruptly, as soon as you can.”

The driver glanced down at his new wad of bills, then shrugged. Whatever you say, spoke his gesture.