At Weather Station Nine, atop a mountain people climbed only out of necessity, Lina had lived alone for three months with a wind gauge, a radio set, and a grey cat that hated noise.

Her job was simple: read the instruments every hour, record the numbers, and send them to the center in the capital. In winter she paid closer attention, because the valleys below could fill with water in minutes when rain fell on the sky far away from her.

One December evening, while she was making tea, the radio set gave off a crackle. No one was supposed to be on that frequency. Then the voice came:

"Lina, listen to me and don't interrupt. Don't trust gauge number four's reading at nine o'clock."

Lina froze where she stood, the cup still in her hand. The voice was her own. Her tone, her way of holding her breath before a sentence. But it sounded a little older than her, and tired.

She pressed the transmit button and asked, "Who are you?"

No answer came. The set went quiet, nothing but static.

She told herself that isolation plays tricks on the mind. Then she glanced at the clock: five minutes to seven. She wrote down exactly what she'd heard in her logbook, and added a note: "Possible hallucination due to isolation."

At eight the radio crackled again, and the same voice came:

"It isn't a hallucination. I told you before I'd prove it to you. The old typewriter in the storeroom is going to start up in three minutes. Don't be afraid."

Lina went to the storeroom, her heart pounding. She sat down in front of the rusty typewriter she hadn't touched in weeks, and watched her watch. One minute passed, then two. On the third minute exactly, the typewriter struck a single letter on its own: "L."

There was no one there. No wind. Just one letter on the yellowed page.

She trembled. Then she understood something else: everything she'd been told had been precise. And the voice speaking to her knew what was going to happen before it happened.

At five minutes to nine, Lina sat in front of gauge number four, staring at it. This gauge measured rainfall in the southern area, where a narrow valley ran through a hiking trail.

At nine exactly she read the number: zero. No rain. Zero millimeters.

She remembered the warning. But everything on the instrument said conditions were normal. And that was the frightening part. If she trusted the gauge, she would signal the center that the weather was safe.

Lina opened the map of the area. Then she noticed something: the map showed a group of hikers registered on the trail that evening — ten people, with a guide. And the water level in the nearby streambeds had been rising slowly for half an hour, by an amount almost too small to notice.

She picked up the microphone and said to the radio, steadily, "If you're me... tell me what to do."

The answer came seconds later: "The reading is wrong. The gauge freezes on cold nights and sticks at zero. Twelve kilometers up, rain has been falling for an hour. The water is heading toward the valley. You have forty minutes. Warn the guide now."

Lina didn't ask twice. She called the guide on the emergency frequency. The reply came a few seconds late, then a garbled voice: "This is the trail group. Go ahead."

She said, "Leave the valley now. Climb to the north ridge. Don't wait. Water's coming."

The guide said, "The sky is clear!"

She said, "I know. Please believe me. You have forty minutes."

Forty-two minutes passed in which she didn't move from her spot. Then the voice came from the radio, this time the guide's own voice, stammering from shock: "The water's reached us... the whole valley is water. We were up on the ridge... everyone's fine. How did you know?"

She didn't answer. She switched off the set and sat on the floor, letting out a breath she'd been holding for hours. The grey cat came and curled up in her lap.

At midnight, as she was straightening her logbook, a question occurred to her that she'd never asked herself before: where had the message come from in the first place?

She thought about it for a full hour. There was no other station, no other set, no one else who knew the station's frequency. The voice had been her own. The sentence it said at the start, "Don't trust gauge number four's reading," was the exact sentence she would have said to herself if she'd known.

She understood. No one had been sending her a message from the future. She was the one who was meant to send it.

She checked the clock: ten past midnight. She had the rest of the night ahead of her to work out how to make the message, what words to use, in what tone. Because someone, somewhere, someday, would need to hear a familiar voice telling them: "Don't trust the instrument. Trust me."

She picked up the microphone, pressed record, and said in a calm voice:

"Lina, listen to me and don't interrupt..."