tic tic tic tic… Tiny noises of compression, sounding through her skull.

She'd been alarmed, the first time she'd heard them, over the noise of her breathing and the tinny wheezes of the scuba gear which sat on her back, wrapping its plastic limbs round her and jamming rubber and metal into her mouth. Now she just listened to the ticking noises, imagining they were the signature of some erratic internal metronome; the unsteady beats of a tiny, bony heart.

The noises were her skull's reaction to the increasing weight of water above her as she dived, descending from the unsteady mirror of the surface, through the warm waters of the lake, to the muddy floor and the stumps of the long-dead trees.

She had held a skull once, and seen the minute fissures marking its surface; tiny hairline cracks stretching from side to side and end to end, jagged valleys on an ivory planet. They were called sutures. Plates of bone grew and met while the baby was still in the womb. The bones jammed together and locked, but left one area free so that the infant's head could pass through its mother's pelvis, producing the spot on a baby's head which remained soft and vulnerable until the bones had clasped there too, and the brain was safe, locked in behind its wall.

When she'd first heard the noises in her head, she'd thought it was caused by those bone-plates in her skull pressing harder in against each other, and the noise travelling through those bones to her ears… but then Philippe had disillusioned her; it was the sinuses which produced the faint, irregular clicking sounds.

It came again, like some slow abacus. tic tic tic…

She pinched her nose and blew, equalising the pressure on either side of her eardrums.

Deeper; she followed Philippe down, keeping his slowly stroking flippers a couple of metres in front of her, conscious of her rhythm matching his, her legs moving through the water in time to Philippe's. His white legs looked like stocky, strangely graceful worms; she laughed into the mouthpiece. The mask pressed harder into her face as they continued down. tic tic…

Philippe began to level out. She could see the lake floor clearly now; a crumpled, grey landscape fading slowly away into the gloom. The old tree stumps poked up through the mud, flat eruptions of drowned life. Philippe looked round briefly at her, and she waved, then levelled out too, to follow him along the water-buried surface of the land, over the sliced trunks and the slow bursts of mud produced by his flippers. tic.

The pressures equalised, the column of water above her and the fluids and gases of her body achieving a temporary equilibrium. The warm water moved against her skin in silky folds, and her hair ruffled behind her in the slipstream of her body, stroking the nape of her neck.

Settled into the pace of swimming, balanced and lulled, flying slowly over the slow settlement of a near-century, following the just-tangible turbulence of the man's wake, she let her mind wander.

She felt — as she always did, down here — untied from the commonality of breath that was the air above. Here, however briefly, she was free. It was a freedom with its own many and precise rules — of times and depths, atmospheres and experience, maintained equipment and weights of air and it was a freedom purchased through surrender to the technology that was strapped to her back (clicking and hissing and burbling) but it was freedom. The air in the mouthpiece tasted of it.

Under the waves, with the skull adjusted. Headlong through the warm waters, like an easy and continual birth. Swimming like flying; the one buoyant image of her fear she could accept.

This had been rainforest; the trees had grown in the wind and the sunlight, and trawled the air for clouds and mist. Now they were gone, long turned to planks and rafters and ribs and seats. Perhaps some of the great trees were pulped, and became paper; perhaps some were turned into sleepers for the railways that helped the canal be built; perhaps some formed the buildings in the Zone, and perhaps some became small ships; boats that had plied the lakes. Sunk, their waterlogged timbers would nestle in these shaded depths, rejoined. Maybe some became musical instruments; a cello, even! She laughed to herself again.

She listened for more tics, but heard none.

She followed the man. In a few strokes and kicks, she knew, she could pass and out-distance him. She was stronger than he knew, perhaps she was even stronger than he was… but he was younger; he was a man, and proud. So she let him lead.

In a few minutes, hypnotically over the drowned forest, they came to what had once been a road. Philippe stopped briefly, treading water over the muddied track, raising clouds of soft grime beneath him while he studied the plastic-wrapped map. She drifted nearby, watching his bubbles wobble their way to the surface. His breath.

He put the map back under his T-shirt, nodded down the road and set off. She kept pace. She knew the gesture he'd just made, and knew the sort of grunt that accompanied it; she imagined she'd heard it translated through the water. She followed him, thinking dreamily of whale songs.

Before they found the village, they heard the noise of an engine. She heard it first, and hardly thought about it, though some part of her was trying to analyse the noise, put a name and a key to it. She realised it was engine noise just as Philippe stopped in front of her, looking around and up, and holding his breath. He gestured to his ears, looking at her; she nodded. They stared up.

The shadow of the boat's hull went past, not overhead but a few tens of metres to their right; a long dark shape dragging a twisted thread of bubbles after it. The noise of its passing grew, peaked, then fell away. She looked at Philippe once the boat had passed, and he shrugged; he pointed down the road again. She hesitated, then nodded.

She followed Philippe, but the mood was different now. Something in her wanted to go back to the Gemini. The inflatable they'd set out from was moored a hundred metres away, in roughly the direction the boat had been heading. She had wondered if the noise of the boat would alter after they'd passed, telling her it had slowed and stopped at the Gemini after all, it might look as though it had been abandoned — but the boat seemed to have continued on beyond that, heading for the middle of the lake and the ships anchored there.

She wanted to go back, to return to the Gemini and then to the ships; to find out what that boat was doing, and who was on it.

She didn't know why she felt so nervous, so suddenly full of a low, nagging dread. But the feeling was there. The war might be coming to touch them at last.

The drowned road dipped, and they followed it. tic tic she heard, diving deeper. tic tic, as they swam towards the ruins.

When Hisako Onoda was six her mother took her to a concert in Sapporo; the NHK Orchestra playing works by Haydn and Handel. Hisako Onoda was a restless, occasionally recalcitrant child and her weary mother suspected she'd have to remove the squirming, wriggling, and quietly but insistently complaining child before the end of the first piece, but she didn't. Hisako Onoda sat still, looked straight ahead at the stage, didn't rustle her bag of taka rabukoro, and — instead, incredibly — listened.