“When I first learned about Cassiopeia,” I say, thinking of that night camping with Mom and Tristan and his dad, “I was so mad when Tristan’s dad told me that it’s known as the W constellation. I thought it was an M.” I arc my arm, making a huge M across the sky. “You know, for Mercedes.”

“Let’s pretend it is. M for Mercedes and M for Mattie.”

I smile in the dim glow from the Boardwalk. “That’s what Tristan’s dad said.”

“He sounds nice.”

An M for Mercedes. “He is.”

Mattie continues, almost to herself, “My stepdad is pretty nice, too.”

I look up at Cassiopeia again. “Technically, Tristan’s dad isn’t my stepdad.” I pause. “But maybe it doesn’t matter.”

“It doesn’t,” Mattie says confidently. “Who cares what anyone is technically? I mean, I have this whole new family who’s not even related to me.”

I nod. She’s right, I suppose. I think about how Tristan’s dad isn’t mine, but he’s still part of my family. Sometimes even more than Mom. And Tristan is still my favorite little brother ever.

“You know what?” Mattie says. “I’m not going to tell anyone you’re my half sister anymore.

My head snaps to stare at her. What? Is she embarrassed of me now? My shoulders tense and my hands curl into fists.

She grins as widely as the hippo on her sweatshirt. “I’m going to call you my sister.”

And my hands relax. My shoulders release. I look over at Mattie. My sister. We lock eyes for a moment. Our matching pairs, eyes that look a lot like Frank Gómez’s eyes.

“You’re a dork, Matilde.”

And we both collapse into giggles, hysterical. We laugh until we can’t laugh anymore. When our laughter dies down, we can hear the whistling sound of the wind as it skims the water. The screams from the roller coaster and the tinny music from the arcade float across the sand. My sister and I catch our breath and study the sky, all those stars.

“It’s funny,” Mattie says after a moment, “the sky here is the same as the sky in Minnesota. When I look up, I feel like I’m home.”

She can’t see me in the dark, but I nod.

“I think the sky is like a book,” I say. She doesn’t say anything, but I know Mattie agrees. “You open the book, and the pages in front of you could take you anywhere. Endless possibilities.”

She sighs. “It’s like a story that’s just beginning.”

ACKNOWLEDGMENTS

As with all books, this one couldn’t have happened without many supportive people. Thank you first to my agent, Thao Le, and my editor, Amanda Ramirez, for letting me write another sibling story.