Second Sister

by Chan Ho-Kei

“You must know this program well, as the librarian,” said N.

  “It’s much easier now than it used to be. We don’t have to bother with stamped cards and so on. I heard that one time, a librarian set the stamp wrong, so all the books we lent out that day had the wrong due date. Now everyone just gets an email as soon as the book is borrowed, and when the book is due, they’ll get a text message to remind them.”

  “That’s convenient and environmentally friendly. But there must still be morons who don’t understand technology and think stamped cards is simpler.” N glanced mockingly at Nga-Yee. She bit her tongue, though she wanted to protest that she understood these systems just fine—it wasn’t very different from what she did at her own library. It was only the internet, which seemed to change every single day, that confused her.

  “Violet, do you know if there’s anything Siu-Man wanted?” N got the conversation back on track. “We don’t know if there was anything troubling her at school, and while we’re here, we could help fulfill her final wishes.”

  Violet spent a few seconds thinking, but finally shook her head. “I don’t know. I’m sorry. We really weren’t that close.”

  “That’s all right, don’t worry about it,” said N. “Siu-Man left very suddenly and was tormented by rumors beforehand, so we thought there might be something we could do for her now.”

  Violet said nothing, just nodded.

  “Apparently your teachers said you weren’t allowed to talk about these rumors, but I’m sure everyone did it secretly … Oh, did anyone in school particularly dislike Siu-Man?”

  Violet looked at him blankly, nonplussed.

  “I keep thinking she must have made an enemy, if someone wanted to blacken her name like that. All those lies—” N sighed. “If she really did offend someone, we’d need to find this person and thaw their heart. Only then will Siu-Man be able to rest in peace.”

  “Well …”

  “Yes? You’ve thought of someone?”

  “I can’t be certain, but I think Lily Shu had some beef with her.” Her voice shrank to a whisper—it seemed she wasn’t happy speaking ill of her classmates. “They used to be good friends, the sort who hung out all the time, but then they suddenly stopped speaking.”

  “So you think Lily was the one spreading these rumors?”

  “I don’t know for sure, but I’ve seen a lot of friends turned enemies, and they do the most horrific things. These days, with the internet, it’s so easy to twist the truth.”

  It was a shock to hear Lily’s name, though of course N had warned Nga-Yee that she and Kwok-Tai might be the liars. Right away, her warm feelings and trust for Lily evaporated.

  “You have a point,” said N, looking sad. “She spent a lot of time in the library. Did you ever see her chatting with other classmates? Maybe I could speak to them too.”

  “She was always alone,” said Violet. “Other people stay to do their homework here, but not many, and everyone keeps to themselves. The library’s quiet after hours—people mostly come here to read magazines or to charge their phones once the classrooms are locked.”

  Nga-Yee understood how she felt. She was passionate about reading too, but most young people would rather read internet garbage than crack open a book. Some American institute did a study showing that the average person read fifty thousand words online each day—practically a whole novel.

  “Could we have a look around the library? I’d like to see what Siu-Man’s daily life was like.”

  “Of course.”

  N thanked Violet, then led Nga-Yee away from the counter as the girl went back to her book. Nga-Yee made a beeline for Siu-Man’s usual seat and touched the table in front of it, as if she were standing by her sister’s side. A buried memory surfaced: Nga-Yee at the folding table in their house, helping her eight-year-old sister with her homework.

  A ringtone sliced through the silence, bringing Nga-Yee back to reality. She looked up to see N across the room, scrabbling for his phone.

  “Sorry,” he called to Violet before hurrying out the door. Nga-Yee wondered if she should follow, but he waved for her to stay. She’d never have expected N to pay attention to library rules, but then her eye landed on Violet and she realized he was still inhabiting the role of a nice guy related to Siu-Man—for social engineering purposes.

  Now that she’d been roused, Nga-Yee didn’t allow herself to sink back into her memories. She wasn’t here to commemorate Siu-Man, but to find out the truth. She sat in Siu-Man’s usual chair and looked all around. She’d vaguely expected to notice some kind of clue, but this seemed like a perfectly ordinary school library. The shelf closest to her had history and geography books, then language and literature below that, all arranged according to the Chinese library classification system. On the wall above the computers to her left was a poster for a “Secondary School Top Readers” competition, a list of magazine subscriptions, and news about recently acquired books. The only notice unrelated to the library was from the school admin, reminding students to exercise caution online, safeguard their passwords, and so on. Ultimately, though, it seemed unlikely that many students paid attention to these bits of paper, whether they were about “New Books” or “Web Safety.”

  Nga-Yee felt a sudden stab of loneliness. She thought about the hubbub as the volleyball team practiced, and the commotion in the rehearsal room. The stillness of the library made it feel removed from the world. Her solitude slowly froze over, squeezing the life from her body. Was it the library or the light streaming through the windows that made her feel this way? Or was it that she couldn’t help thinking about Siu-Man?

  Her sister had once sat right here, trying to escape everyone’s notice, head bent over her books.

  “Had enough? It’s time to go.”

  She turned to see N behind her. She hadn’t noticed him coming back in. She stood and said a silent goodbye to the spot.

  “Thanks for your help, Violet. We’re going,” N called out. The girl put down her novel and nodded. Nga-Yee noticed the title—Kanae Minato’s Confessions—and wondered if it was suitable for a fourteen-year-old.

  “Do you think Violet was right, that Lily and Siu-Man were enemies? Could Lily be the culprit?” Nga-Yee asked as soon as they got to the staircase, where no one would hear them.

  “You really are easily swayed, Miss Au,” said N. “Violet told us your sister had a falling-out with a good friend. That doesn’t make her friend a killer.”

  “Did you find any clues in there?”

  “Yes, but not enough to draw conclusions, so there’s no point telling you. What do you think?”

  “About Violet To? I like her, to be honest—she’s an introvert who enjoys reading. And I’m a librarian too, so we have that in common—”

  “I’m not talking about the To girl.” N stopped walking and turned to face her. “You met your sister’s classmates today and heard how they felt about her. You walked through the same spaces that Siu-Man once did, sat where she sat, and saw what she saw. What do you think the difference is between the real Siu-Man and the one in your head?”

  Nga-Yee didn’t understand the question. “Siu-Man is Siu-Man, that’s all.”

  “Forget it. Pretend I never asked.” N pursed his lips, making it clear he didn’t think it was worth explaining anything to her. He turned and stomped away. Nga-Yee had no idea what she’d said to get the cold shoulder. She could only silently curse this arrogant bastard.

  “Do we need to meet anyone else? What about the other iPhone owners on the list?”

  “No need. We’re leaving now.”

  “The investigation’s over?”

  “It’s continuing, but let’s talk about it when we’ve gotten away from here.”

  “We should at least say goodbye to Miss Yuen—”

  “No point. You want to tell her we’re leaving? That’s not going to make her happy, and she won’t appreciate your good manners. Worst-case scenario, she might start wondering why we’re still here and what we’ve
been doing.”

  “Miss Yuen wouldn’t—”

  “Fine. You speak to that woman. I’m going home. Up to you whether you come with me.”

  Nga-Yee had to give in and follow him. The investigation was much more important to her than whether Miss Yuen thought her rude.

  They returned their badges at the gate, then walked down Waterloo toward Nathan Road. N led the way. As Nga-Yee trotted behind him, she wanted to ask what their next step was, but she kept her mouth shut.

  “Let’s grab a coffee there.” They were on Nathan Road, almost at the MTR station on Pitt Street, when N pointed at a sign up ahead: PISCES CAFÉ. This turned out to be on the second floor of a skyscraper. Rent was expensive in Yau Ma Tei and Mong Kok, and the only way an independent café could survive was to give up a street-level entrance. A sandwich board on the ground floor listed the opening hours, with an arrow telling them where to go. The coffee shop’s logo was two fish in a green circle, suspiciously like the Starbucks mermaid, though it seemed unlikely that anyone would mistake this place for the global chain.

  They went up the stairs. Inside, the furniture and color scheme were also Starbucks rip-offs, down to the self-service counter.

  “Medium iced latte,” said N to the barista. He didn’t ask Nga-Yee what she wanted, but by this time she hadn’t expected it. She glanced at the menu and blanched at the prices: coffees started at thirty dollars, and even the cheapest item, a cup of tea, would cost her twenty. She was still living on the eight-hundred-dollar loan from Wendy, but she wanted to find out more from N, so had no choice but to stump up twenty dollars for a cup of tea that couldn’t have cost more than two to brew.

  It was still before three o’clock, so the coffee shop was mostly empty. N brought his iced latte to a corner table, and Nga-Yee followed with her hot beverage.

  “Okay, now can you tell me if we’re done for the day?” she asked urgently.

  N chewed on his straw and took a sip of latte, then pulled the white phone from his pocket. As he tapped at it, he said, “I didn’t tell you before, but there’s another reason we were at the school.”

  “What’s that?”

  “To make sure that kidkit727 is one of your sister’s schoolmates.”

  “Hadn’t you already deduced that?”

  “That was just a deduction. I’m talking about evidence now.” He looked up. “Conclusive evidence. Remember what I said before, about the emails kidkit727 sent from MTR stations?”

  “Yes, those things—what do you call them?—IP addresses.”

  “And I told you an IP address is like your queue number at the bank or hospital. You have to get one each time you go in. Remember?”

  Nga-Yee nodded.

  “So when you get online using Wi-Fi, another string of numbers gets recorded by the provider. To go on with the bank analogy, that’s like having to produce your ID to prove you’re who you say you are, and only then will they give you a queue number—or IP address.”

  “ID?”

  “Yes, a number that’s unique to you.” N pointed at the phone in his hand, then at the public telephone by the counter. “Every device with Wi-Fi capability has a media access control address, or MAC for short, assigned by the manufacturer. To put it simply, there are ten million smartphones in use in Hong Kong, which means there are ten million MAC addresses. Like human fingerprints, no two can be identical.”

  “What does that mean?”

  “When I was looking up the IP addresses kidkit727 used to get online, I also found out the iPhone’s MAC address: 3E06B2A252F3.” N rattled off the numbers and letters without blinking.

  “3E—”

  “3E06B2A252F3. In theory, all we have to do is find an iPhone with this MAC address, and we’ve found kidkit727.”

  Nga-Yee almost jumped to her feet. “Then let’s go back to the school right away and look up the MAC addresses of all eighteen iPhone users!”

  “Already done.”

  “And?”

  “First, let me give you a lesson about wireless technology. Do you know what Wi-Fi is?”

  “It lets a tablet or phone get online without being plugged in,” said Nga-Yee. After N told her that Siu-Man had been sent those emails over Wi-Fi, she’d found a book in the library with a simple explanation of this technology. Unlike most people, she still preferred getting her information from books.

  “When you press the button telling your phone or tablet to connect to the Wi-Fi, what happens?”

  Nga-Yee stared at him. The book had only talked about how to use it.

  “I knew you’d have no idea. But to be honest, most smartphone users don’t know either. All they need to do is pick out the right network from a list and click on it.” N gestured at a sign behind the counter. “Can you read what that says?”

  Nga-Yee turned her head. FREE WI-FI, read the sign, and below it, ID: PISCESFREEWIFI.

  N placed Siu-Man’s phone on the table and pulled up a list: CSL, Y5Zone, Alan_Xiaomi, and so on. Next to “PiscesFreeWiFi” it said “Already connected.”

  “These others are nearby networks. Think of them as overhead cables that all connect to fiber-optic lines underground. Your phone connects to the network, which connects to the fiber-optic line beneath the ground. With me so far?”

  Nga-Yee nodded.

  “This is the bit most people don’t notice. Why do you think all these names appear? CSL, Y5Zone, and so on?”

  “The phone gets them from somewhere? Like a radio picks up certain stations?”

  “Half right. The networks send out their own names and other data, and when your phone is within range, they’ll connect. The part you got wrong is that your phone is also sending out signals all the time, and even if you aren’t online, it still exchanges data with nearby networks.”

  “Huh? Doesn’t that only happen when you tell it to connect?”

  “No. The machines already exchange quite a bit of information before you get to that point. And even if it’s already connected to a network, it still sends out a signal from time to time, to see what else is out there. That’s known as a probe request. It’s like saying, ‘Hi, I’m a cell phone, are there any networks I can talk to?’ When the networks hear this, they send out a probe response: ‘Hi, I’m PiscesFreeWiFi, I’m available.’ And that’s why its name appears on your phone.”

  “Okay, I get it now. But why do I need to know all this?”

  N put the little white phone on the table next to Siu-Man’s red one. “While we were at the school, I set my phone to be a hot spot the whole time, so it made a record of all the probe requests around it. Oh, I forgot to say: one of the pieces of information collected by a probe request is the device’s MAC address.”

  Nga-Yee looked at the rows of text on the white phone’s screen. One of them had been highlighted: “3E:06:B2:A2:52:F3.”

  “We walked right past kidkit727’s cell phone earlier today,” said N simply.

  “Was it Lil—Lily?” Nga-Yee stuttered. She thought about the iPhone on the cafeteria table.

  “Going by the time log, the MAC address was picked up starting when we met Lily at her classroom. But that doesn’t mean it was her. It could have been someone else around there, or even someone upstairs or downstairs—Wi-Fi signals can pass through walls and ceilings.”

  Nga-Yee realized what N was hinting at. All three iPhone-owning suspects had been within range the whole time: the Countess in the fourth-floor rehearsal room, Violet To in the fifth-floor library. Perhaps they’d been in the cafeteria too, even if Nga-Yee hadn’t noticed them. And with volleyball practice taking place on the ground floor, Lily’s phone would have been in the vicinity.

  “So our suspects are Lily, Violet, and the Countess.”

  “Not necessarily, but I first picked up the signal in the classroom, so we need to focus on your sister’s classmates.”

  “Why not necessarily?”

  “Two reasons.” N took a mouthful of his latte. “First, we can’t eliminate the possibilit
y that kidkit727 just happened to be somewhere else in the west wing. It doesn’t make sense to restrict ourselves to the suspects we’ve already spoken to.”

  Nga-Yee nodded, though she still thought it was probably one of those three.

  “Second, not to pour cold water on this idea”—N smiled grimly—“MAC addresses aren’t like fingerprints. They can be changed.”

  “Oh?”

  “As long as you have the right software, you can alter your MAC address. Given the way the iPhone 5S is set up to be compatible with iOS 8, you could make your phone send out a random fake MAC address to probe requests and use the real one only when it’s actually connecting to Wi-Fi. Apple says they enable this to protect their customers’ privacy, but many of their rivals think it’s just another way of giving them a monopoly over data.”

  “So today was a waste of time,” said Nga-Yee.

  “No, no, no,” said N, flashing a smile at her. “Just picking up 3E06B2A252F3 at the school takes us a big step ahead. Even if a new iPhone was sending out a decoy MAC address, the chances of randomly generating this particular one are one in 280 trillion. In other words, impossible.”

  “But you just said it could also be changed deliberately.”

  “Yes. Remember, our main enemy is the Rat, who’s hiding behind Little Seven as he helps her with his tech knowledge. He could be trying to lead the investigation in the wrong direction by showing Little Seven how to use a fake MAC address when she sent those messages to your sister, the same way she made use of the MTR station Wi-Fi. These programs are easy to use. With the right guidance, even you could learn how in five minutes.”

  “So I was right?” asked Nga-Yee, puzzled.

  “You still don’t understand. We’re facing two possibilities now: if the Rat didn’t help Little Seven disguise her MAC address, then we can identify Little Seven from her phone.”

  “And if he did?”

  “Then Little Seven is trying to frame whoever has the 3E06B2A252F3 phone—otherwise why not just use a random number?”

  Nga-Yee understood. “So, no matter what, we have to track down the owner of that 3E-whatever phone. Either that’s our culprit, or it’s someone our culprit wants to set up.”