River rests a hand on my arm. “You’ve got to let go of what you had as a family—before the pills, before the wave. Honor it, but let it go. You can’t hold on to the past, Mae. It’s gone. Something new will grow in its place, but you have to make space for it. At the same time, you can’t live in the future. Because then you miss out on now. And now is the only thing you’re guaranteed. You’re a scientist, you know this stuff: It’s the nature of existence. Everything winks out. Including, someday, you. We have to be okay in the face of that.”

“I can’t lose her,” I say, my voice breaking.

The smile River gives me is kind, a smile from the other side of a journey I don’t want to be on.

“My love, she was never yours to begin with.” She reaches out, wipes my tears away.

Somehow, in the past few months, I’ve learned how to cry.

“You’re telling me to give up on her,” I say. “Give up responsibility. So I just let my sister be addicted so I can live my great life in the present moment and enjoy her for the short time we have?”

She shakes her head. “It sounds like apathy, like we choose inaction, but that’s not what I’m saying. The chaos of life is still there, and we are still living and hoping and dreaming and loving and helping. But we aren’t ruled by the chaos, by our fear of what might happen in the future. And we don’t believe the lie that we can somehow control the chaos. That’s impossible—it’s chaos: by definition, not controllable. And once you realize that you, Mae Winters, can’t control the outcome of your sister’s addiction, there’s freedom—in the chaos, you can be free. To show up for this day, this moment, this sister. Right here, right now. You can’t control this ride—hers or yours. But how you take the ride, that’s up to you.”

“But what if … what if you’re all alone on the ride?”

River’s eyes stay on mine as she speaks, and it makes me feel like a captain on a boat, steering toward a distant horizon. “You’re not alone, Mae. Not really. Your love for your sister, your parents—my love for my brother—and the love they have for us: That’s for keeps, my friend. No matter what happens, through all the impermanence of things, that’s for keeps. It’s what makes the ride worth taking—even if there’s sometimes an empty seat next to you.”

The train slows and she raises her hands to adjust her scarf, and I see those words tattooed on the sides: ONLY LOVE.

“Hah-vahd,” the announcer calls over the speaker.

“Your stop,” she says.