Liz Leyden is a writer living in New Jersey.

Strong winds ground the helicopter, so the ambulance drives my friend to the hospital, the one that will keep her until the lungs either arrive in time or don’t.

Aimee survives the three-hour trip. She’s at the top of the transplant list. I’m relieved; I’m terrified. How close to dead do you have to be to earn the No. 1 spot?

More than 113,000 people — babies, grandmothers, best friends, brothers — need organ transplants to save their lives. Signing up to donate is simple: Check a box at the DMV, or skip the lines entirely at organdonor.gov. It seems so obvious to share what we have when we no longer need it, an act of generosity in death that leaves a trail of life behind. Yet not enough of us do; every day in the United States, 18 people die waiting.

Aimee’s wait is near its end: What she needs now depends on strangers.

In second grade, my family moved into the house beside hers. From my bedroom window, I could see the oak tree where later we’d whisper secrets. We shared a classroom and a school bus and had last names that were also next-door neighbors. Ours was a friendship born of geography.

But at first, we fought. About friends and hide-and-seek rules and toothpaste. Aimee’s name was spelled for her French Canadian roots. I noted that it also matched the toothpaste with the catchy commercial: “AIM tastes good!” chirped the kid on TV, and one day on the playground, that’s what I sang.

As a taunt, it wasn’t so clever, but it caught her attention. Eyes blazing, she chased me on skinny legs until her fingernails raked my arm. She was always tough.

Did I know then she was sick? In a way. Every day, a few minutes before lunch, she left class to visit the nurse. Every day, she picked a friend to go with her. Eventually, I was one.

We walked the empty hallways, tracing our fingers along the walls, sneaking peeks in classrooms where the other kids sat stuck at their desks. I hated when she chose anyone else.

Liz Leyden, right, and her best friend, Aimee. (Courtesy of Liz Leyden)

While Aimee saw the nurse, I waited outside the door. It never occurred to me to wonder what happened while she was out of sight. Did she sip medicine? Take a pill? Get a shot? Forty years later, I finally asked her dad as we sat beside her hospital bed. It was a pill, he said.

I thought about that pill, swallowed every day without complaint. The thick silence of the hallway, that feeling of stolen magic, just the two of us, prickled my skin like it was yesterday. Back then, being sick seemed lucky.

But cystic fibrosis was just one part of her. And the older we got, the harder it was to remember what it meant, because most of the time, it was hard to remember she was sick at all.

When she was 17, she flew alone from New York to Hawaii to visit her great aunts. She studied hard and skied black-diamond slopes and collected friends and kept in touch with all of them. She adventured in Paris, became an accountant and toured the Pyramids. She got to parties early and stayed late and rescued cats and had kids. She ran and ran on those skinny legs, rain or shine, every day, to keep her lungs strong.

And she coughed — a reminder, a warning. But it was easy to ignore, to believe that she was tough enough to keep the disease at bay. Because of the way she lived, it was easy to forget she was dying.

Aimee would hate that sentence. She — who, aged 10, laughed when I cried during “E.T.” — would roll her eyes at the sentimental sound of it. Too squishy. Too soft. She’d be right. (But so am I.)

I bring “Little House in the Big Woods,” her old favorite, to the hospital on her third day. The tracheotomy tube dangling from her neck delivers her oxygen now. She mouths hello when she sees me. I have heard her say it a million times; I can hear her say it now.

I hold up the book. She nods, closes her eyes. I begin to read. A house made of logs, venison smoking over hickory chips. It is a world away from this room high above the Hudson River.

The month before, we’d walked slowly around her block. It was drizzling, the street quiet but for chirping birds and the sharp staccato bursts of her breath. She was mostly housebound, tethered to an oxygen tank as mucus crept across her lungs and steadily choked her of air. But there she was, in the rain, a portable tank on her back.

“At least you’ve seen me run a half-marathon,” she said.

On our third loop, the tank needle hovered near red. I asked if we should turn back.

“I think I can make one more,” she said. And she did.

She walks the hospital hallways once a day, would do more, but too many therapists are needed to push the machines keeping her alive. When the staff is off on Sundays, she is upset but makes do with leg lifts in bed.

The skin across her cheeks has grown tight, but her spirit is entirely intact. She reaches for her whiteboard anytime doctors visit, even when her eyes are shut.

Her handwriting is wobbly, but her questions — about carbon monoxide levels and whether any lungs are on the horizon — are sharp. Is she thinking of her kids? Crunching numbers, weighing whether her body will last? She is a widow. Her husband had cancer. It wasn’t supposed to be like this.

She is constantly assessed: blood drawn, chest X-rayed, a camera scoped into her lungs to monitor what’s left. On the eighth day, a machine begins removing carbon dioxide from her blood because her lungs no longer can; the blood is pumped out a thick tube in her neck and returned, oxygenated, through an artery in her groin.

I head north to watch her kids while her mother visits. Friends don gowns and gloves to sit beside her. One prays in the hospital chapel each time she leaves.

The calendar turns a page. Trees begin to bloom. On the 19th day, the call comes: A pair of lungs is available. The morning passes. Her father receives the verdict: The surgical team has rejected them.

“You don’t want the wrong lungs,” I say, hating the words. She looks so tired. I hug her as I leave. It’s not enough.

She gets up and walks the next morning, listening to the Beastie Boys, aiming for the hallway overlooking the city. She studies photos of her kids and messages on cards taped to the wall: “Love is the best medicine” and “There is a light at the end of the tunnel.”

I think about the racetrack where we worked in high school and the ever-shifting odds, tallied until the moment the betting windows closed. Numbers are the thing to beat.

More than half of adults in the United States are registered to be organ donors, but only 3 in 1,000 people die in a way that allows for their organs to be donated. In 2018, there were 36,529 organ transplants in the United States, including 2,530 lung transplants.

On her 24th day, Aimee gets hers.

Before the surgery, doctors and nurses celebrate a moment no one had been sure would arrive. One nurse cries. Tears of joy. They have watched her determined steps.

I hug her goodbye, but, for the first time in a month, believe it might not be for good. Outside, I sit on a dirty curb near an ambulance, and I finally cry.

Two months later, I’m standing beside her parents in her kitchen. One of my sons tells her she was like the British during the Blitz: Even when it looked bad, she kept fighting.

She laughs. She is exactly the same. Except she can’t hug anyone or touch certain foods. Except she can laugh and laugh without choking on a cough.

For a lifetime, Aimee ran. When she couldn’t run, she walked: through the neighborhood, around the block, along a hospital hallway, one foot in front of the other.

At lunch, her mother sits next to me.

“Isn’t it amazing?”

It feels like a dream.

My friend looks at us, at me, and groans.

“You saw the ugly,” she said.

She’s right.

It was ugly.

But she was beautiful.