The tide gauge had been reading backwards for six minutes.
Surveyor Second Class Nneka Adaeze noted it in the log, then noted the time, then looked at the gauge again. The float sat at its upper stop. Water pressed against the outside of the survey post’s lower window in a wall of brown-green silence, which was consistent with submersion. The number on the gauge said the tide was going out.
She adjusted the line in the log. Instrument fault or instrument correct: undetermined.
“Okafor.” Senior Surveyor Tomasz Okafor was on the far side of the post, feeding the light-line back onto its spool with the methodical patience she had come to understand meant he was thinking about something else entirely. He looked over. She showed him the gauge without saying anything further.
He crossed the room, considered the number, considered the window, and wrote something in his own log. His pen moved in small, economical strokes. “When did we last have a correspondent reading from the surface?”
“Forty minutes. Before submersion.”
“And the post’s elapsed clock.”
“Forty-three minutes.”
He said nothing immediately. The post groaned — the deep structural kind, pressure differential, the sound she’d had to teach herself not to flinch at. Through the lower window, something pale drifted past. She had stopped cataloguing the pale drifting things two hours ago when the tally had reached thirty-one and she could not determine if they were the same objects recirculating or new ones.
The door to this world opened in a sea cave on the home side, a cold coastal shelf the Compact had held sealed for eleven years pending what the older records called hydrological reassessment. What that meant, practically, was that the survey team before hers had gone through and not come back, and the Compact had waited what it calculated was a sufficient interval, and then sent Okafor. Okafor had requested a second officer, which was standard. He had specifically requested her, which she was still deciding how to feel about.
The city was genuine. That much was past dispute. It covered the sea floor in every direction the external lamp reached — dressed stone, colonnaded, intact in the way that meant not ruined so much as deliberately kept. Someone had built here when the ground was dry, or had built for the water from the start. The architecture did not help her determine which. She had sketched fourteen distinct building forms and labeled all of them purpose unknown.
“The recommendation question,” Okafor said. He had the abstracted tone he used when he was not asking her to answer, only to listen.
“Quarantine,” she said anyway.
He looked at her.
“We don’t know what the tide gauge means,” she said. “We don’t know where the previous team is. We don’t know if the city is inhabited currently or was inhabited previously or is being — ” she paused, found the word she wanted, ” — maintained. Any one of those is sufficient.”
“They are.” He turned back to the gauge. “The question is whether we file from here or from the home side.”
That was the question. The post had a relay spike they could drive into the door’s threshold and bounce a signal through — the Compact would receive the recommendation within hours, could dispatch a seal team within days. Or they could pull back through the door and file in person, which protocol preferred, which the previous team had presumably tried to do.
“How much of the city haven’t we covered,” she said. It was not quite a question.
“Eighty-three percent, by conservative estimate.” He picked up the light-line spool again. Set it down. “There’s a structure at grid seven-four that the lamp caught the edge of. Larger than anything we’ve documented. Intact roof. What looks like a powered light source.”
She looked at her own log. The entry for grid seven-four said anomalous return, investigate, and she had written it three hours ago and they had surveyed in the other direction since.
Through the upper window — above the waterline by three meters, just barely — she could see the door’s anchor light, the fixed orange point the Compact required survey teams to maintain. It was where it should be. The door was where it should be.
“Two hours,” Okafor said. “Grid seven-four. Then we file from the home side regardless.”
“Regardless,” she repeated, and wrote it down.
He was already checking the rebreathers. She watched him test the seal on his, the precise quarter-turn of the valve, the way he held it to his face for a count of three before he was satisfied. She had seen him do it with the same count every time.
She tested her own. Turned the valve. Counted.
The tide gauge still read outgoing.