The Last Wake

Tovan's body had been swimming behind Roa for four circuits.

It could not overtake her. That was by design. The suit took the pressure of Roa's wake, converted it into a flexion beneath Tovan's ribs, and ended each movement an instant before the water could push him out of phase. Roa's spine registered that correction as a brief pressure between her shoulder blades. As long as she stayed in front, he would keep his distance.

The others left the formation as they passed the white vent. First Varo, who had shared the seabed campaigns with Tovan; then the two women from the algae gardens; then those who knew him only from repairing seals. Each stopped kicking, spread their arms, and rose towards the lights of the houses. The body they had preceded completed one more movement and began to descend through the mineral plume.

Tovan went on.

Roa circled the vent. She felt the pressure of his late correction. She had recognised it thousands of times while travelling: Tovan always arrived half a beat late, then pretended the delay was a decision.

Varo peeled away without speaking. For a few metres he stayed to Tovan's left; then he stopped moving his legs. The body did not turn towards him. It continued behind Roa.

The vent expelled pale water from the black seabed. Mineral particles rose around them and turned every wake into a visible ribbon. Beyond the circle, Lerna's ocean began where the floodlights ended: darkness without up or down, except for the houses floating two hundred metres above and the pressure of a body behind her.

When the swimming spines were installed, Tovan had hated the name.

“A spine gives orders,” he used to say. “This listens.”

The device did not read thoughts or choose a course. It registered how the suit bent, including the curvature a neighbouring wake imposed on the body, and shortened the next impulse to bring it into phase. The city crossed kilometres of darkness using less energy because every swimmer listened with their back to the person ahead.

Now Tovan's brain emitted no signal. The suit's stimulator retained a minimal pattern, and the water supplied the rest.

Roa completed the fifth circuit.

The delayed pressure returned between her shoulder blades.

“He isn't choosing you,” Varo said from above.

“I know.”

Roa accelerated slightly. Tovan accelerated. She tightened the curve and felt him cut inwards too. The suit registered the water's deflection, used it to interrupt one impulse, and fired the next.

The first time they travelled with the spines, Tovan spent an hour trying not to follow her. He changed rhythm, slipped out of the wake, came back from below.

“A body that can save energy shouldn't mistake comfort for agreement,” he had said.

Roa replied that the ocean did not ask for consent before it pushed. He smiled inside his mask and took his place behind her. On the way home, Roa felt the late correction and knew, without looking, that he was still there.

Later they invented a gesture for saying no without leaving formation: two quick impulses and one long one. A spine could bring a speed into phase, but that irregularity forced the swimmer behind to choose between copying it and losing the wake. Tovan chose to lose it. He would reappear a few metres below, pleased as if he had proved something about freedom.

Once he did it during a nine-hour migration. Roa was leading three other people and could not leave the line without making them spend their own reserves. Tovan stayed below, swimming to a rhythm that helped no one. She saw him appear at the edge of her visor, made small by the dark. Every few minutes she slowed until the whole formation complained over the channel; he recovered the wake, rested, and pulled away again.

When they arrived, they argued while their legs shook for opposite reasons: Roa's from towing four bodies and Tovan's from insisting on paying for every impulse.

“I don't need you to agree,” she said. “I need to know where you are.”

Tovan placed his hand between her shoulder blades, exactly where the suit registered the swimmer behind.

“That's where you find me when I give in.”

“That's where I find you when you follow.”

They never resolved the difference. They learned to travel inside it.

He did the same thing at home. All Lerna's lamps dimmed when the gardens demanded more power. Tovan had isolated the one above their table. Every evening, for a few seconds, the whole room darkened except for that yellow circle.

“It doesn't save anything,” Roa would say.

“It isn't there to save. It's there so you notice that the others obey.”

When the city recovered its brightness, he switched off his lamp by hand.

The body behind her now could neither pull away nor switch anything off.

Roa made the gesture: two quick impulses and one long one.

Tovan shortened the first, corrected the second, and let the third carry him. He did not lose the wake.

Above them, the swimmers who had finished the rite formed a broken circle. The women from the gardens rose hand in hand. Varo floated motionless beside the lowest lights. No one descended to interrupt her.

On Lerna, the last person swam ahead of the dead until they stopped producing a wake. Then the suit could no longer find an external curvature with which to order its impulses, and the body descended towards the warm fissure.

Tovan had found the name of the rite cruel.

“The last wake always belongs to the one who's alive,” he said when they buried his mother. “The other person only receives it.”

That time he had been the one in front. Roa watched from above as he completed three circuits and moved aside with one clean motion. His mother's body lost its rhythm, spread its arms, and began to descend. Tovan rose without looking back.

That night he admitted that he had counted to a hundred before opening the formation. Roa did not know which hurt more: that he had lied with the clean movement, or that he had thought it necessary to confess.

The sixth circuit closed.

The particles drew Roa's wake and then Tovan's, almost overlapping. The water seemed to remember the same body twice. Only on the curves did they separate: his ribbon opened by a hand's breadth and returned late.

Roa looked at the telemetry. Tovan's suit showed no initiative, only the sequence implanted before they descended. Self-flexion. Neighbouring pressure. Interruption. Impulse. Four terms that turned the body into grammatical continuity.

Roa was the one who had asked to preserve it.

Tovan died in his sleep, with no water around him. The house detected the absence of breath and lit a yellow light that Roa mistook for the kitchen filter. She found him on his side, one hand beneath his cheek, the other closed on the sheet. There was no last sentence. The isolated lamp was still burning above the table.

Roa switched it off before requesting the rite.

The suit now gave her what the room had not: a consequence for every movement she made.

She tilted one shoulder and the body tilted its own. She accelerated and felt it draw closer. She widened the curve and the pressure between her shoulder blades diminished, but did not disappear.

She could prolong it until some number decided for her. She could call a limit what she did not want to choose.

Roa slowed.

Tovan drew closer. The suit was designed to maintain phase, not an exact distance. When the current weakened, the body behind used what remained and closed the gap. Roa felt a hand brush her heel.

She slipped aside.

Tovan completed one impulse and hung suspended beside her. With no wake in front, the suit waited. Particles rose between them and at moments erased the misted mask.

Roa placed a hand on Tovan's chest. The suit registered the contact as weight, not rhythm. Nothing happened until she moved again.

“You didn't agree,” she said.

Her own voice returned through the bone of her face.

She took the forward position again. One kick was enough for Tovan's suit to find her pressure, interrupt the wait, and complete the next movement.

Two quick impulses and one long one.

Tovan followed.

Roa completed half a circuit. At the point where they usually turned towards the northern wall, she made the first quick impulse. The body corrected. She made the second. The body corrected again. Instead of the third, Roa turned upwards and crossed through her own ribbon of particles.

The wake dissolved.

Tovan continued with the minimal pattern for two movements. The first carried him towards the centre of the circle. The second found no external curvature to interrupt it. His legs completed the impulse and remained extended.

Roa could return to the position ahead of him. She only had to descend a metre. The suit would feel her pressure again.

She did not.

The white plume took Tovan's body. At first he descended on his side. Then the weight of the regulator righted him and he became vertical, arms spread. Particles covered the mask. The suit's glow diminished until it looked like one of the luminous bacteria rising from the fissure in the opposite direction.

Roa waited until she could no longer see him.

Then she swam towards the houses without activating collective listening. Her suit offered her three nearby wakes: Varo, one of the women from the gardens, someone she could not identify by their light. She rejected all three.

She moved more slowly. Every impulse cost her in full.

Halfway up, she made Tovan's gesture: two quick movements and one long one. No one occupied the position behind her. There was no body to choose between copying it and losing the wake.

For the first time since they descended, the water did not return her final movement.

Scientific note

This story draws on version 1 of *A spinal circuit for collective coordination*, by Laurence Picton and thirteen co-authors, submitted to arXiv on 26 August 2026.

The paper combines electrophysiology, calcium imaging, optogenetics, and behavioural analysis in zebrafish with a neuromechanical model and a robotic fish. The authors describe spinal proprioceptive neurons that detect body bends produced both by the fish's own swimming and by a neighbour's wake, then adjust the phase of the locomotor network. When that circuit is disrupted, the fish retain the ability to swim but lose phase matching, school cohesion, and polarisation. In the model and robot, the loop is sufficient to match a wake and reduce energy use.

The authors infer that some immediate coordination can emerge from local interactions without central control. Sufficiency is shown in constructed systems where the loop is the only source of coupling. The complete animal probably integrates descending signals, vision, smell, hearing, and lateral-line sensing; the study is limited to zebrafish and does not establish a universal mechanism of collective behaviour.

Lerna, the human spines, post-mortem motor stimulation, the rite, the characters, their messages, and all their specific behaviours and causal chains are fictional compositions. The paper neither describes nor predicts this technology and does not show that an equivalent circuit governs human coordination.

Read the preprint on arXiv