The Atlantic. Eleven Hours.

The cabin dims twenty minutes after takeoff.

Not dark — that particular aircraft darkness that is its own category of light, the kind that exists nowhere else. Overhead panels fading to a bruised blue. The small reading lights making islands of yellow along the rows. Outside the oval windows, nothing. The Gulf of Mexico has no features at night from this altitude. Just the absence of city.

Sofia has the window seat. She always takes the window seat.

She is not sleeping yet. She is in the specific suspension of early long-haul — past the drink service, past the headphone adjustment, past the choice of film she will not finish. Just sitting. The white noise of the engines at cruising altitude is a particular frequency she has stopped hearing consciously, the way you stop hearing air conditioning in a room you've been in long enough.

Her carry-on is in the overhead. The small black case is inside it.

She has not thought about the cold chain since boarding. This is intentional. There is nothing to do about it at 36,000 feet. The compounds are stable at cabin temperature for twenty-four to forty-eight hours depending on the compound. The flight is eleven. She will be at the hotel in Nice by afternoon. She has done this calculation already, on the ground, before the door closed. Now it runs in the background.

Some anxiety is useful. Cold-chain anxiety on a plane is not.

Somewhere over Cuba — she estimates this from the flight map she checked briefly before the screens went to ambient — she feels the first wave of it.

Not tiredness exactly. A softening. The particular signal her body sends at around midnight Miami time: we are done now. It is consistent. Has been consistent for years. She has started to think of it less as sleepiness and more as punctuality. The body keeping its appointment with darkness.

This is the cortisol completing its descent. The melatonin beginning its climb. The system switching registers — from absorption, repair, movement, to consolidation, restoration, stillness. Everything in sequence. Everything on time.

On Miami time.

Which is the problem she will spend the next six days solving.

She wakes once, somewhere over the mid-Atlantic.

The cabin is in its deepest dark now. Most passengers horizontal or attempting it. The engines unchanged. Her mouth is dry — the humidity in commercial aircraft cabins drops to roughly fifteen percent at cruising altitude, lower than the Sahara, and she has learned to drink water before sleeping rather than waiting to feel thirsty. She drinks from the bottle she brought. Closes her eyes.

The man from the departure gate is three rows ahead. She noticed when boarding — not him specifically, but the same quality of stillness, the tablet, the absence of headphones. He had the aisle seat. He was already asleep by the time the seatbelt sign went off.

She finds this faintly interesting. People who can sleep immediately on planes have either made peace with something or learned to stop fighting things they cannot change.

She does not know which it is for him.

She closes her eyes again.

The truth about this flight — about any long eastbound flight — is that the body does not know it is happening.

There is no sensation of crossing a timezone. No signal. No notification equivalent. The suprachiasmatic nucleus, the cluster of neurons behind the eyes that keeps biological time, is reset by one thing primarily: light. Specifically the quality of light at dawn, entering through the retina, triggering a cascade that resets the twenty-four-hour cycle.

In darkness, at altitude, over the Atlantic, with the windows sealed and the cabin in artificial twilight, the body receives no such signal.

It continues exactly where it left off.

Miami. Midnight. May 19.

This is the biological fact that changes everything about traveling with a protocol. The wall clock is already running six hours ahead of where Sofia's body is. By the time she lands in Nice, the gap will be the same — six hours — and it will remain approximately six hours until her system begins its slow eastward drift, one hour per day, across the days that follow.

Eastbound is always harder than westbound. The body has a natural preference — its free-running period is slightly longer than twenty-four hours, which means it leans west naturally, prefers to stay up slightly later, resists moving forward. Ask it to advance six hours and it complies, slowly, reluctantly, one hour per day.

Six days minimum. More, for some people. More, when the travel is east.

She sleeps again, properly this time. The deep architecture of it — the slow wave, the stillness, the growth hormone pulse that happens in the first ninety minutes if the body trusts the darkness enough to commit. She has taken Ipamorelin before boarding. Its job is here, now, in this darkness, in this committed stillness — amplifying what the body is already trying to do. The compound needs sleep architecture to work. Sleep architecture needs the body to believe it is night.

Her body believes it is night. Her body is correct.

In Nice, it will be 06:00 when they land.

Her body will believe it is midnight.

Both things will be true simultaneously, and only one of them will matter for the protocol.

The descent begins before light. The cabin brightens artificially — the airline's attempt to synchronise passengers with destination time, the overhead panels shifting from bruised blue to something approximating morning. A flight attendant moves through the rows with a practiced efficiency that suggests she has done this particular route many hundreds of times.

Sofia raises her window shade.

The Mediterranean appears below in the early light — that specific blue-grey of the sea before full sunrise, the coastline of the Côte d'Azur beginning to resolve from the haze. The terracotta and the white. The curve of the bay that painters came here specifically to paint and kept returning to even after they could not explain why.

It is genuinely beautiful. She registers this without sentimentality. Travel has not made her cynical about beauty. It has made her precise about it.

The wall clock on her phone says 06:12. Nice. UTC+2. Her body says 00:12. Miami.

She glances at the app. A single line:

Day 1. Dose window: 12:00 local. Your cortisol peaks at biological morning.

She puts the phone away.

The man three rows ahead is awake. She notices him close his tablet. He looks out his window at the same coastline with the same particular quality of attention — not tourist attention, not the performed wonder of someone experiencing something for the first time. The attention of someone who has seen this view before and still finds it worth looking at.

The wheels touch the runway at 06:31.

Her body is still over the Gulf of Mexico, keeping its own time, carrying everything forward that she has built into it — the rhythm, the sequence, the careful accumulated continuity of months — into a morning it does not yet recognize as morning.

Six days.

One hour at a time.