The Doorbell in Aisle Nine

At two in the morning, a doorbell rang in aisle nine.

Osei stopped pushing his trolley of tinned soup. The sound was not a soft chime. It was a loud, bright ring, like the bell on a front door. It bounced between the tall shelves of pasta and rice.

"Did you hear that?" he called.

Jabu came around the corner with a craft knife in her hand. She was seventeen, the same age as Osei, and she had worked the night shift for three weeks. "I heard it," she said. "That's the fourth time tonight."

"Maybe it's a parrot," Osei said. "The day manager left a note. A customer saw a bird near the front doors yesterday."

"Parrots don't sound like doorbells."

"Some of them do. They copy everything they hear."

Jabu listened. The ring came again, exactly the same, with the same sharp second note. A real bird would have changed it at least once. "That's a machine," she said. "A bird would get bored."

"Then why is it so loud?"

"I don't know. But we've been told to find it before the delivery lorry arrives at five."

Osei sighed. The store was almost empty at night. Only the freezers hummed, and the lights over the empty aisles buzzed like sleepy insects. Nobody had ever told him that a supermarket could feel so large. "All right," he said. "Let's find it."

They started with the simplest plan. They stood in the middle of aisle nine and waited for the next ring. When it came, they walked toward it as fast as they could.

The sound seemed to come from the left. They hurried to the end of the aisle and found only a stack of empty boxes. Then the bell rang again, and now it sounded like it came from behind them. They turned around. Nothing was there.

"This is stupid," Jabu said. "The sound is bouncing off the shelves. It's coming from everywhere."

They tried again in aisle ten. Then in aisle eight. Each time, they ended up in the wrong place, with a wrong guess and sore feet. After twenty minutes, Osei sat on a crate of washing powder and put his head in his hands.

"My first plan has completely failed," he said.

"It was your plan?" Jabu asked.

"I just said we should walk toward it. That counts."

Jabu laughed, then stopped. She was looking at the ceiling, where the speakers were. "What if the sound isn't from the speakers at all?" she said. "We've been guessing by ear. Ears are bad at this."

"What else do we have?"

She took her phone from her pocket. "Two phones. Yours and mine. If one hears the ring a moment before the other, that tells us which way it comes from."

Osei raised his head. "That's actually clever."

"I watched a film about submarines last month. Don't tell anyone."

They switched off the music and the little radio in the staff room. They even unplugged the drinks fridge by the door, which made a loud rattle. Then they put their phones on the floor at two ends of the aisle. The phones were thirty metres apart. They pressed record on both.

The store became very quiet. Osei could hear his own heart. He felt silly, standing still in a shop with his arms folded, waiting for a ring.

Then it came. The bright note rolled down the aisle, and both phones caught it.

Jabu played the two recordings side by side on her screen. The lines of sound looked like two small mountains. "Look," she said. "Your phone heard it first. Not by much. A tiny bit."

"So it's closer to my end."

"Closer to your end, and low down. Your phone is on the floor, and the sound is stronger on it than on mine."

They walked to Osei's end and knelt on the cold tiles. There was a big pallet of dog food there, wrapped in plastic. The delivery team had left it for the morning shift. Behind it, in the narrow gap against the wall, something blinked a small yellow light.

"There," Osei whispered.

They moved the pallet together, pushing it with their shoulders. The plastic squeaked. In the gap sat a small grey machine about the size of a cat. It had four soft wheels, a flat top and a tiny screen. One of its wheels was stuck in a loose strip of tape from a box.

"It's a stock robot," Jabu said. "The kind the big stores use. I've seen them on videos."

"Our store doesn't have one."

"It does now."

The screen on the robot showed a sad little line of text. It said, "BATTERY LOW. NO HUMAN FOUND. RINGING FOR HELP." Then the doorbell rang again, so loud that both teenagers jumped.

Osei put his hands over his ears. "It's ringing because it can't find anyone!"

"We were in the next aisle the whole time," Jabu said. She pulled the strip of tape from the wheel. The robot wiggled and rolled forward a little way, then stopped and rang again.

"Make it stop," Osei begged.

"I'm trying." Jabu turned the machine over. Underneath, there was a flat panel with a row of tiny symbols. One of them showed a plug. Another showed a bell with a line through it. "I think this one is the quiet button."

She pressed the bell symbol. The ringing stopped at once. The silence that followed was so deep that Osei laughed out loud.

"Now it needs power," she said. "There's a charging spot in the back office. The manager's keys are hanging by the door."

They lifted the robot together. It was heavier than it looked. Osei carried the front and Jabu carried the back. They walked slowly through the dark store, like two people carrying a sleeping child.

In the office, they found the charging mat under a pile of paper. Jabu put the robot on it. A green light came on, and the small screen changed its message. It said, "CHARGING. THANK YOU, NIGHT STAFF."

"It knows who we are," Osei said.

"It knows the job we do. That's different." Jabu looked pleased all the same. She picked up a sheet of paper from the desk. It was a letter from the head office, and she read it with a frown. "Listen to this. 'The new stock robot will arrive on a trial basis. Please keep it in the back office until training day.' It has been lost since Tuesday."

"So the day manager's bird was this?"

"A customer must have heard it ringing near the front doors. People think the strangest things."

Osei checked the clock on the wall. It was ten to four. They had an hour before the lorry came. He felt tired, but he also felt proud. They had solved a real puzzle together.

They went back to aisle nine and finished the soup. They worked in a comfortable silence. Now and then Osei glanced toward the office, where the green light glowed through the glass.

At five o'clock the lorry arrived. The driver looked at the two tired teenagers, and he looked at the empty shelves they had filled. "Quiet night?" he asked.

"Very quiet," Jabu said. "Mostly."

When the driver went outside, Osei turned to her. "Do we tell the day manager about the robot?"

"We'll leave her a note. A very short one." Jabu grinned. "I'll write that the parrot has been caught."

"Fine," Osei said. "But if that machine ever learns to sing, I'm quitting."