In the school yard there grows an apple tree.

Its lower branches have been shaved to prevent the children clambering on it. In the autumn it showers the students with small, tart fruit. In the summer it blooms, and its tufts of white petals are like banks of cumulus clouds.

It's blooming now.

The little boy sits among the swaying upper branches, one arm is looped around the tree trunk, the other tugs at his forelock. His nose is bloody.

Below him, the children point and shout and laugh, the adults buzz and clamour around the base of the tree. They shout his name and demand he comes down. The boy shakes his head and will not move. A ladder is fetched and is found to be too short. Should they call the fire service? Should they call his father?

The other little boy slips into the yard. He is smaller and darker than the first, and goes unseen by the dithering adults. He stands in the yard for a little time only, staring up at the tree, then removes the thick, cableknit jumper he wears, and when no one is looking, slings the jumper over the lowest branch, and uses it to pull himself into the apple tree.

As people notice and stop and point, he climbs, sure-handed, up through the clouds of blossom, until he is right at the top, among the tree's perilously slender upper branches. He slides out onto the topmost branch, and the other little boy, wary at first, slides over to make room for him. The two of them sit, shoulder to shoulder and hip to hip. They speak in low voices.

They stay there for a long time.

They stay there while the adults wheedle and cajole and argue among themselves. They stay as the other two boys arrive into the yard at a run, and the older has to collar the younger to stop him making a dash on the tree too. They stay there as the sleek black sedan pulls up at the kerb.

She was not there.

She was not there, but she sees it just the same.

She sees it through a thousand different fractals, through scraps of footage uploaded from phones, through teachers' reports written days later, through extrapolations from weather satellites cruising overhead, GPS signals, personal comm devices and emergency service records, she takes them all and piece by piece, and like something seen through the compound eyes of Musca Domestica, a thousand images form a single coherent picture. One that only she can see.

The apple tree is precious to her in the same way that a supernova is precious to her. It is something that is gone from the universe, that burned away many years ago, yet whose light can still reach her.

For EOS the apple tree will bloom forever.

Time passes. Virgil goes on missions. Brains takes over routine maintenance. There will likely be a written exam before he is allowed to work on Two again.

His father's words, what he thought of him, what EOS blurted out, unthinking, hurts like a kick in the teeth.

It's unfair that sometimes the person you are mad at won't even afford you the luxury of still being here to let you be mad at them. Instead you end up mad at everybody else. Instead you end up mad at yourself.

More time passes. He cools off. The wound scabs over, a little anyway. Scott makes him do supply runs, which – touché, Scott – is exactly what Dad used to do to Scott when Scott was being moody and difficult.

It's the shame that kills him, the shame of being laid bare. It's knowing that the worst things you think about yourself, the people who know you best think them too. How can he joke with Gordon, or help Alan with his chemistry, or bully Scott into looking after himself when he feels like this? He wants – he just wants to be left alone for a little while.

EOS does not return.

One day he returns late from a supply run. The hangar outside is dark. From the sky he could see that the others are out by the pool.

He moves the yoke into docking position. He listens to the engines cool.

Thunderbird Two is a song.

A song he knows so well that the changes in it are enough to tell him he is no longer alone.

"Go away, John."

John ignores him, pulls open the aft hatch, slides inside.

He and John don't talk that much anymore. That's a thing that's old and new and complex and tied up in Dad and Scott and the people they were before they lost their father and the people they are now. They are an efficient team, and Virgil loves his brother and knows that John loves him, but John has never been one to seek out other people anyway, and in the last few years Virgil hasn't pushed back the way he should, the way he once might have.

But anyway, John's here now.

He drops into the co-pilot's seat, and looks around, as if this is a brand new perspective. It probably is. Virgil can count on one hand the times that John's been part of Two's mission crew. "You're not going to say it's smaller than you remember, are you?"

A soft woof of laughter, then silence. He stares straight ahead, but he can still see John's face reflected in the glass and he can see that John's watching him too. He looks worried. "Please can you make this right?"

Virgil groans softly. "You suck at this, Johnny."

"I know." A beat. "I usually have you to do it for me."

"I know."

John clears his throat. "Whatever EOS did –"

"She didn't do anything." He looks over at John, and gives him a smile, the same one he gives small children when the water is rising and their parents are nowhere out there in the dark. "It'll be fine."

Of course, it's John, so he's not fooled one bit.

He stands and claps an arm on Virgil's shoulder, and from John, who is almost never the one to initiate a touch, this means a lot. "She misses you, Virg. She's not the only one." He sets a thumb drive down on Thunderbird 2's console. "She asked me to give you this. I'll be upstairs. When you need me."

Virgil waits until he's gone.

He picks up the thumb drive, flips it over and touches the drive to his display.

Instantly a hologram springs up. It's a 3D rendering of a tree. Cherry, he thinks, or maybe apple. White blossom clings to it like flurries of snow.

At first he thinks it must be a painting, that she has sent him a piece of art. But when he looks closer he can see the knots in the wood, the imperfections, the bald patches where the lower branches were hacked off close to the trunk to prevent people climbing on it. This is a real tree.

And then he sees two boys, one dark, one red gold, sitting at the top of the tree.

Suddenly the air is full of the smell of apple blossom. He remembers the blood under John's fingernails, the rust coloured scab around his left nostril, John sitting in the wreckage of his ruined astrolabe and begging Virgil not to tell Scott. And how he had heard from a classmate later that 'some freak' was hiding up a tree. He remembers sitting on that branch until his legs were numb and how John talked for hours about cloud nebulas until he was ready to come down.

The image of the tree is changing all of a sudden, becoming subjective and out of focus, the view masked by milling heads, the perspective becoming that of someone watching from the ground up.

"Well, Boss, what do you want to do?" It's like an electric shock surging through him. He would know that voice, those clipped polished tones, anywhere, though he hasn't heard it in years. It's Kyrano. "Do you want me to go up there and get them?"

He hopes that Kyrano's perspective will shift, that he'll turn, but Kyrano, or at least his body cam, stays pointed at the tree, and as much as Virgil strains, all he can see is the sleeve of a dark woollen coat of the man next to him.

"No," says a voice, achingly, painfully familiar, "Virgil will get him to come down. Virgil always does."

He doesn't know how to make it right.

But he knows a little bit about songs.

The songs he writes are gentle things, meant to be hummed and strummed and quickly forgotten.

But not this song.

This song is filled with the roar of engines, with the strange distant majesty of stars, the thrill of danger and the frission that comes with a job well done. It's got each of his brothers in it, and Kayo, Brains and Lady Penelope and even a quick little riff that is probably Parker. It's a song about loneliness, about wandering the world alone and afraid, and how the world changes when you have people who care for you. It's a song about home.

It takes him forty-eight hours to write, stopping only for a snatch of sleep and, once, to rescue a couple of lost Sherpas.

It's the best thing he's ever written.

But that's beside the point.

When he's done he sends it to John with a note, "For EOS."

Then he goes downstairs.

His brothers and Brains are eating breakfast at the kitchen island.

"Brains, Thunderbird Two's rear thruster is running a little hot. I'm going to go have a look at it. Oh, and I know you like the idea of the seven point relay but it's making the controls sluggish during deceleration. We're going back to the five pointer. I'll be in the hangar if you need me."

He leaves again.

"Did he just correct Brains on his Thunderbird design?" asks Gordon in a voice of mixed awe and terror.

"We're all gonna die," is Alan's pronouncement.

He spends the morning in the hangar, tuning up his girl's engines. It feels good. It feels right.

Thunderbird Two is a song.

And he knows the changes in it like he knows his own heartbeat.

He grins as a familiar harmony joins the melody.

"Hullo, EOS."

"Hello, Virgil Tracy.