Mercedes groans. “No, archaeologists dig up human bones. You’re thinking of a paleontologist.”

I can feel my face get hot. Now Mercedes is going to think I’m so dumb. When, actually, I do know the differences between archaeologists and paleontologists. Goes to show that I’ve been spending too much time with a five-year-old boy. If my mom had never married Bob, none of this would be happening. I wouldn’t have new stepbrothers. I would never have moved to California. And I never would have met Mercedes.

“He’s not a paleontologist and he’s not an archaeologist. He’s an anthropologist. He studies, um…” She pauses. I realize that she might not know what an anthropologist does, either. “They study humans, not dig up bones,” she says at last. “Like, culture, human behavior, that kind of thing. Anthropologists watch people, learn all about them by seeing what they do.”

We watch a woman in track pants and a long-sleeved shirt that says Run Like the Wind jog through the park. Whenever I see someone jogging in their neon shoes and track clothes, I wonder if they’re running toward something or away from something.

“That’s his job?” I ask after the woman passes. “That’s pretty cool. I knew he was in Colombia, but I didn’t know about him being an anthropologist, him being in the jungle. Why do you think he’s never come to meet us?”

Mercedes shrugs like she never really thought about it. “My mom said Frank Gómez couldn’t handle having kids, what with living in the jungle all the time.”

“My mom never said anything about him having another daughter. She must not know,” I say. It’s not a question, but I wish Mercedes could answer it.

Instead, she asks, “Does she ever talk to him?”

“Like on the phone?” I shake my head. “I remember that when I was little, she got a letter from him. That’s it.”

“Well, maybe he told her about Mom and me in that letter.”

“She would have told me,” I insist.

“Maybe she lied.”

I think of how much my mom hates lies. When she lost her job, she told me, “You know I never liked that marketing job. There’s so much dishonesty in advertising. And I hate lying to people—even little lies, even lies by omission. Lying is a terrible thing, Mattie. Each time you tell a lie, you lose a little part of yourself.”

“She would never lie to me,” I say to Mercedes.

I can tell Mercedes doesn’t really believe that. I wonder who lies to her. I wonder who she lies to. She shrugs. “Then maybe she doesn’t know.”

“I can’t believe it.” I’m not sure which part I can’t believe. That my father is a famous arc—I mean, anthropologist? That I have a half sister? That my mom never told me or never knew?