Du Mei brought breakfast in a paper bag and refused to look at his conclusion.
“Show me what you received.”
They were at the small table in his apartment. Her bicycle helmet occupied the only clear chair, so Yanchuan moved a stack of unopened mail onto the floor. Mei worked two streets from his office, teaching machines to recognize faults in factory images. They had met when her system confidently classified a shadow as a broken seal and he had been the engineer asked to explain the lighting.
She had never forgiven him for being right about it. He had never forgiven her for fixing it before he finished explaining.
Now she made a fresh copy of the files and read his brother’s note twice.
“Did he send the raw samples?”
“Only the extract in the second workbook.”
“Then we say extract. We don’t call it raw because it looks inconvenient.”
She put both time columns beside each other. The first sheet summarized settled operation. Its rows were regular and complete. The second included a change in load, a protective intervention, and a period during which several fields were marked unavailable. A note at the bottom said the averages excluded invalid intervals.
“That can be legitimate,” she said.
“The missing values?”
“Excluding them. If you explain what the remaining average means.”
Yanchuan watched her highlight the header. The summary was called Full Acceptance Run. Beneath it, in smaller type, a footnote narrowed the claim until it described something else.
They tried the harmless explanations first. Local time against recorded time. A clock offset. A different sampling rate. None accounted for the selection by itself. When Mei aligned the event markers, the trouble sat between ten o’clock and fourteen minutes past. One chart began its tidy comparison after the intervention. The other retained enough of the transition to show that the equipment had not behaved tidily.
“So they removed fourteen minutes.”
“The report leaves them out,” Mei said. “We don’t yet know who selected the window, or why.”
He pushed his bowl away. The difference seemed almost insulting. His brother was missing, and they had found a small argument about a spreadsheet.
Mei noticed. “What did you expect?”
“I don’t know.”
“A map?”
He said nothing.
She softened her voice. “There isn’t a location hidden in this. He wanted a second opinion. We can give him one.”
They reconstructed the two plots without filling the missing fields. The line broke where the information broke. It was ugly. It was also the first picture that let Yanchuan see the limits of what they had.
He remembered Yansheng repairing a toy excavator for his son. One wheel had gone missing. Rather than pretend the toy was finished, he had handed it back with a little paper flag attached: awaiting part. The boy had played with it for another hour.
“Someone signed that header,” Yanchuan said.
“A signature in a copy,” Mei replied. “Ask for the original acceptance package and its revision history. And the device event log. Through the people entitled to request them.”
He began an angry email. Mei watched him delete its first paragraph.
The final message listed three differences, attached a marked working copy, and asked Luo to preserve the source records. He copied An. He did not attach the entire family chronology or accuse anyone of causing a disappearance.
Luo replied within twenty minutes: Technical questions should be directed to the supplier. The company is concentrating on staff welfare.
An answered before Yanchuan could. Please provide the supplier contact and confirm who holds the original records. These questions do not replace the missing-person inquiry.
Mei read the reply over his shoulder.
“Your sister-in-law should be running this table.”
“She already is.”
It was nearly noon. His apartment had become hot despite the open window. Downstairs someone was arguing with a courier about a parcel marked delivered.
Mei packed her laptop. At the door she stopped.
“Don’t make me the person who proves what you need to believe.”
He wanted to tell her he would not. Instead he looked at the broken line on his screen and understood why she had asked.
“Tell me when I do,” he said.
After she left, he renamed the plot. Not evidence_of_fraud. Not last_clue. He called it comparison_with_gaps, put the date after it, and sent it to An.