But it seemed to me that she was just going through the motions. I wondered if she was looking for a sign, something she couldn't find with us or even at Yale. She stayed in this funk all the way through graduation. In mid-​June she went to stay with her friend Mindy's family at the beach and got a job renting out beach chairs by the boardwalk every day.

Three mornings into it she met Adam. He was down at the beach on vacation with some friends from the show, and rented a chair from her. He stayed all day, then asked her out. I could tell when she called the next morning, her voice so happy and laughing over the line, that our Cass was back. But not, we soon learned, for long.

I don't think any of us knew how much we'd needed Cass until she was gone. All we had was her room, her stories, and the quiet that settled in as we tried in vain to spread ourselves out and fill the space she'd left behind.

Everyone forgot my birthday as our kitchen became mission control, full of ringing phones, loud voices, and panic. My mother refused to leave the phone, positive Cass would call any minute and say it was all a joke, of course she was still going to Yale. Meanwhile my mother's friends from the PTA and Junior League circled through the house making fresh pots of coffee every five minutes, wiping the counters down, and clucking their tongues in packs by the back door.

My father shut himself in his office to call everyone who'd ever known Cass, hanging up each time to cross another name off the long list in front of him. She was eighteen, so technically she couldn't be listed as a runaway. She was more like a soldier gone AWOL, still owing some service and on the lam. They'd already tried Adam's apartment in New York, but the number had been disconnected. Then they called the Lamont Shipper Show, where they kept getting an answering machine encouraging them to leave their experience with this week's topicMy Twin Dresses Like a Slut and I Can't Stand It!so that a staffer could get back to them.

“I can't believe she'd do this,” my mother kept saying. “Yale. She's supposed to be at Yale.” And all the heads around her would nod, or hand her more coffee, or cluck again. I went into Cass's room and sat on her bed, looking around at how neatly she'd left everything. In a stack by the bureau was everything she and my mother had bought on endless Saturday trips to Wal-​Mart for college: pillowcases, a fan, a little plastic basket to hold her shower stuff, hangers, and her new blue comforter, still in its plastic bag. I wondered how long she'd known she wouldn't use any of this stuff when she'd hatched this plan to be with Adam. She'd fooled us all, every one.

She had come home from the beach tanned, gorgeous, and sloppy in love, and proceeded to spend about an hour each night on the phone long-​distance with him, spending every bit of the money she'd made that summer.

“I love you,” she'd whisper to him, and I'd blush; she didn't even care that I was there. She'd be lying across the bed, twirling and un-​twirling the cord around her wrist. “No, I love you more. I do. Adam, I do. Okay. Good night. I love you. What? More than anything. Anything. I swear. Okay. I love you too.”

And when she finally did hang up she'd pull her legs up against her chest, grinning stupidly, and sigh. “You are pathetic,” I told her one night when it was particularly sickening, involving about twenty I love yous and four punkins. “Oh, Caitlin,” she said, sighing again, rolling over on the bed and sitting up to look at me. “Someday this will happen to you.”

“God, I hope not,” I said.

“If I act like that, be sure to put me out of my misery.”

“Oh, really,” she said, raising one eyebrow. Then, before I could react, she lunged forward and grabbed me around the waist, pulling me down onto the bed with her. I tried to wriggle away but she was strong, laughing in my ear as we fought.

“Give,” she said in my ear; she had a lock hold on my waist. “Go on. Say it.”

“Okay, okay,” I said, laughing. “I give.” I could feel her breathing against the back of my neck. “Caitlin, Caitlin,” she said in my ear, one arm still thrown over my shoulder, holding me there. She reached up with her finger and traced the scar over my eyebrow, and I closed my eye, breathing in. Cass always smelled like Ivory soap and fresh air. “You're such a pain in the ass,” she whispered to me. “But I love you anyway.”

“Likewise,” I said. That had been two weeks earlier. She had to have known even then she was leaving.

I walked to her mirror and looked at all the ribbons and pictures she had taped around it: spelling bees, honor roll, shots from the mall photo booth of her friends making faces and laughing, their arms looped around each other.

There were a couple of us, too. One from a Christmas when we were kids, both of us in little red dresses and white tights, holding hands, and one from a summer at the lake where we're sitting at the end of a dock, legs dangling over, in our matching blue polka-​dot bathing suits, eating Popsicles. On the other side of the wall, in my room, I had the same bed, the same bureau set, and the same mirror.

But on my mirror, I had one picture of my best friend, Rina, my third-​place ribbon from horseback riding, and my certificate from the B honor roll. Most people would have been happy with that. But for me, with Cass always blazing the trail ahead, there was nothing to do but pale in comparison.

Okay, so maybe I was jealous, now and then, but I could never have hated Cass. She came to all my competitions, cheering the loudest as I went for the bronze. She was the first one waiting for me when I came off the ice during my only skating competition, after falling on my ass four times in five minutes.