Night crept over every corner of the city, neon lights flickering.
Though it was barely nine o’clock, the streets were unusually silent.
Occasionally, a car would rumble by, as if rolling through the city centre at the slowest speed.
Tomorrow was Fengtan County’s annual high school entrance exam.
The government had already announced a three-day ban on honking.
The city dimmed its lights early, waiting for the grand parade of students.
The last night’s rest was crucial, and all the examinees had gone to bed early.
The lights were still on in Yu Renjie’s villa. Police had planted phone taps on every floor.
The kidnappers had called at 8 a.m. and again at noon, demanding thirty million in cash and promising to let his son go for the exam the next day.
Yu Renjie and Tang Xiang hadn’t seen their son in days.
They looked utterly haggard, nothing of their old radiance left.
Their clothes were wrinkled, hair a mess, constantly scratching and fidgeting.
They looked like hollow reeds, ready to fall at the slightest breeze.
They’d imagined a ransom of five or ten million, but never expected the kidnappers to open with thirty million, all cash.
Worse, the boy had been taken for days, and the call came on the very last day before the exam.
Yu Renjie tried to sound calm.
“Let me make sure my son is safe. You haven’t hurt him, have you? Let us see him on video, please.”
Of course, the other side refused.
“If we find out you called the police, you’ll never see your son again. Prepare the cash. Wait for my next call.”
A classic, old-school kidnapper routine, just like in countless TV dramas.
He even wondered if it was pre-recorded, with no one actually on the other end.
Crash.
Yu Renjie shook all over, losing control for the first time.
He slammed the phone to the floor, smashing it to pieces.
Tang Xiang wiped away silent tears.
The police could only offer routine comfort, continuing to analyze the audio and trace signals.
At least the call wasn’t wasted—they used surveillance data and previous clues to finally identify a suspect: Dong Tao, with a criminal record, jailed five years ago for kidnapping.
He was careful, though; he’d tossed his first SIM card into someone else’s car, which was now headed for the provincial capital.
Dong Tao’s last sighting was in a massage parlor’s surveillance blind spot, and then he vanished, like a stone sinking into the sea.
With the trail cold again, the police could only keep combing through Dong Tao’s accounts, tracking his movements, searching for possible hiding places, and waiting for the third call.
Liang Mei’s house was also brightly lit.
Most of the people there were from Third Middle School.
As lights went out one by one, even the wind seemed to stop, the leaves silent, the night frozen black.
Only Liang Mei’s home shone like a lone island in a dead sea.
At half past nine, Miaojia and Li Yingqiao were still at the dinner table, poring over wrong answers.
Instant noodles were still on the table.
Li Yingqiao took the chance to wipe the table, then rushed over as soon as Liang Mei put down her phone with a heavy face.
“How is it, Teacher Liang? Something happened to Meow Meow, right?”
Liang Mei’s lips trembled, unsure whether to tell them, afraid it would affect their exams.
Sure enough, the next second, Li Yingqiao saw her hesitate and clung to her arm, shaking it.
“Teacher, please don’t hide it from us. Meow Meow’s message to me definitely means something. If you don’t tell me, I’ll be distracted during the exam tomorrow anyway!”
“Wait, calm down for a minute,” Liang Mei glanced at the clock, making a quick decision.
“I’ll call Teacher Zhu. Write down the two sets of numbers Yu Jinyang sent you. When Teacher Zhu arrives, we’ll try to figure it out together. But you both must promise me—no matter what, you have to go to bed before eleven.”
Li Yingqiao and Zheng Miaojia exchanged a look.
“Okay!”
Zhu Xiaoliang got the call in the middle of the night and rushed over in slippers.
As soon as he walked in, Li Yingqiao and Zheng Miaojia were slumped over the table, staring at the two sets of numbers in frustration.
Zheng Miaojia asked, “Qiaoqiao, how did you know something was off?”
Li Yingqiao scribbled furiously, pen scratching the paper.
“I don’t know. At first I didn’t notice. But after being tortured by Teacher Zhu lately, I see numbers and have to calculate. The more I looked, the more wrong it felt…”
“Any ideas?”
Zhu Xiaoliang walked over, took off his glasses, picked up the sheet in front of Miaojia, and examined it.
“Teacher Liang said he’s been kidnapped for days. When was the message sent? Do you remember?”
Li Yingqiao thought for a moment.
“It should’ve been the second night after he was kidnapped. The first message was 626, sent at ten-thirty p.m. The second was 3364, two seconds later. I got mixed up at first because the messages were in my mom’s inbox, so the later one appeared first. I didn’t check the time and just assumed 3364 came first, so I kept dialing 3364626, thinking it was a landline number.”
“Did anyone answer?”
“It was a dead number.”
Zhu Xiaoliang understood.
He plopped into a chair, grabbed Zheng Miaojia’s pen, and quickly wrote a string of numbers on the paper.
“I don’t have time to explain. If you get it, great. If not, don’t ask. For now, we can only assume this is a distress signal. It could also be that the kidnappers sent it by accident, but that’s unlikely. Usually, when kidnappers get the victim’s phone, they pull the battery right away to avoid being tracked.”
Liang Mei suddenly thought of something.
“Wait, can’t the police track his SIM card? He managed to send a message, didn’t he?”
Zhu Xiaoliang shook his head.
“Not necessarily. Powering up the phone takes thirty seconds to register on the network, so skilled kidnappers will keep it on for less than thirty seconds each time they call or text, then turn it off again. Some even use Faraday cages or clone SIM cards and toss them in recycling bins to mislead police. Crime methods keep evolving. Anyway, discussing that is pointless—”
“Teacher, I have an idea!”
Li Yingqiao stared at the paper filled with calculations.
“If you type 626 on the nine-key keypad, it spells Cat. 3364 on the keypad spells ‘Feng’ from Fengzi Gang. Maybe he’s telling me: Cat is at Fengzi Gang.”
Just back from Fengzi Gang, Zhu Xiaoliang fell silent.
Liang Mei, “…In my humble opinion, with Yu Jinyang’s smarts, he’d probably enter the numbers for ‘Feng,’ ‘Zi,’ and ‘Gang’ separately.”
Zheng Miaojia said, “Or maybe it means ‘cat crazy’—he’s saying he’s lost his mind. It’s a distress signal.”
“…Draw, Miaojia,” Zhu Xiaoliang said.
Li Yingqiao leaned back, arms folded, pen tucked under her nose, staring at the numbers.
“I’ll think some more. If he chose to send the message to me, there must be something I’d recognize.”
But as she thought, she realized there were many things she and Yu Jinyang shared, but almost none related to numbers: Little Painting Town, Fengzi Gang, Shi Dapeng, rolling pin, crayfish, princess carry, Conan…
“He’s good at math, right?”
Zhu Xiaoliang’s first instinct was to try Caesar cipher: FBFCCFD—looked like a useless string of numbers.
“He’s probably the best at math among them,” Liang Mei said.
Zhu Xiaoliang nodded thoughtfully.
“That rules out some answers. Thanks, Teacher Liang, that’s helpful.”
Liang Mei, “…No need, Zhu Xiaoliang.”
But Zhu Xiaoliang was already deep in thought.
“Li Yingqiao, what were you two talking about before this?”
“I told him to return the Conan book Teacher Liang confiscated.
I said I’d greet him with the Fibonacci Sequence so he wouldn’t ignore me.”
Li Yingqiao suddenly thought of something.
“Teacher, you said sunflowers are a classic example of the Fibonacci Sequence. Could it be there are 626 sunflowers somewhere?”
“Then what does 3364 mean?”
Zhu Xiaoliang stared at his notes.
“Is it part of the Fibonacci Sequence?”
Fibonacci Sequence—
Li Yingqiao sat, eyes glued to her notes, trying every way to convert the numbers to text.
She even tried hexadecimal, which gave 5F9244—like a license plate, but not quite.
Teacher Zhu mentioned ASCII, but that just gave a bunch of exclamation marks.
Surely Yu Meow Meow wouldn’t bother replying about her shock at learning the Fibonacci Sequence while being kidnapped.
But she kept feeling there was a connection, 6, 26, 33, 64…
Wait a minute!
Could it really be a sequence?
Time ticked by, and before they knew it, it was ten-thirty.
Yu Renjie and the police still hadn’t received the third call, but at least they’d gotten good news from Liang Mei’s side: his son had sent a message to Li Yingqiao on the second day of the kidnapping, which meant he hadn’t lost hope and was still trying to save himself.
Yu Renjie was still waiting by the phone, fingers drumming on his knee.
The villa door opened, and his grandparents, having rushed over, staggered in.
Seeing the house full of people, they almost collapsed.
They’d never seen so many police at home before, and their voices shook.
“Any news? The kidnappers haven’t called yet? What about the classmate? Were those numbers from Jinyang?”
“Not yet,” Tang Xiang said, exhausted and hollow, her whole body chilled.
“Those kids have their exams tomorrow, but they’re still helping with their math teacher at this hour. We’ll wait for their news. Even if it’s not useful, we’ll be grateful. If it helps, great; if not, that’s fine too. It’s fine.”
She seemed to be comforting her mother, and herself.
Grandma, who’d been vegetarian for forty years, started praying with her prayer beads.
“Good kids, all of them. Jinyang is lucky to have such friends.”
Ring ring ring—
Everyone tensed up at once. Nearly twenty people in the villa, including the expert team analyzing the numbers, all froze, waiting in absolute silence for the father to answer the final call.
Yu Renjie felt feverish; he’d had a temperature since yesterday, sweat pouring down his forehead.
He couldn’t tell if it was nerves or illness.
He licked his dry lips, forgetting how long it had been since he’d had water, scrubbed his face hard, and, with a policeman’s OK gesture, picked up the phone.
“Hello—”
“It’s me. Li Yingqiao just won’t go to bed. If she doesn’t solve this in half an hour, I’ll knock her out and drag her to bed myself. Just letting you know ahead of time.”
In the apartment, several people were still racking their brains.
Liang Mei, who didn’t understand math, was smoking on the balcony to ease her nerves, talking to Aunt Li Shuli on the phone.
Aunt Li Shuli was about to say, “Is this my fault for not seeing the message sooner?” when she heard her daughter shriek with excitement, “Teacher Zhu! The numbers Yu Jinyang sent me are really the Fibonacci Sequence!”
Immediately, Zhu Xiaoliang fired off a rapid series of questions and answers with her.
Finally, Zhu Xiaoliang asked in a serious tone, “Do you know about the classic last-digit cycle in the Fibonacci Sequence?”
“I didn’t before,” Li Yingqiao spread her notes out, thoughts racing.
“You said this wouldn’t be on the test, so I never looked into it. But just now, I worked out the results step by step. The Fibonacci formula is F(n) = F(n-1) + F(n-2), so the first two numbers, 6 and 26, are the starting points. If we use Yu Jinyang’s modified Fibonacci Sequence, it goes: 6, 26, 32, 58, 90, 148, 238… I calculated up to the twentieth term, which is 124210. For every fifth term, the last digit is always zero.”
Liang Mei, just off the phone, came over and repeated, “So the fifth term is 90, ends in zero; tenth is 1010, ends in zero; fifteenth is 11200, ends in zero; twentieth is 124210, ends in zero. Every five terms, the last digit is zero. What does that mean?”
Zhu Xiaoliang glanced at Li Yingqiao.
She put down her pen, looked up at Liang Mei, and said, “Teacher Liang, what in life is cyclical?”
Before Liang Mei could answer, Zheng Miaojia asked, “But what about 3364? That number isn’t in the sequence.”
“3364 is 58 squared,” Zhu Xiaoliang said, putting on his glasses and circling the fourth term on the paper.
“Of all things, Yu Jinyang gave us 58 squared, which just happens to be the fourth term in the sequence. Coincidence? I’ve always said, real math is in life. I’ve never met this student, but he really observes math in the world.”
“Why did he send 58 squared in the second message?”
Liang Mei asked.
Zhu Xiaoliang looked meaningfully at Li Yingqiao.
“She knows.”
“It’s the bus schedule,” Li Yingqiao’s mind was suddenly clear.
She remembered how they’d chased the bus together a few days ago.
“The 58 bus runs every half hour, but there’s another bus that only comes five times a day and stops on request. 58 squared—he’s telling me he rides the No. 58 bus back and forth twice a day.”