“Medusa?” I gasp. I don’t have to think hard to remember that character from mythology. “The snake-haired monster who turned people to stone with her eyes?”

“Same one.” She finishes off her energy drink and tosses the can into a recycling bin. “That’s not the real story, though.”

She acts like that’s the end of it, like that’s all the info I’m going to get. I jab my hands onto my hips and give her my best scowl.

Finally, she sighs and says, “Medusa was a guardian, not a monster. Along with her two immortal sisters, she kept monsters from terrorizing the human world.”

My arms drop. The human world. The earth tilts a little beneath my feet. Why do I feel like, from this moment on, that’s going to have a slightly different meaning?

“And the eyes-to-stone thing?” I force the question out around my shock.

“Pure myth.” Gretchen starts to rub her neck and then winces with pain. “Her eyes had the power to hypnotize—temporarily. Totally harmless.”

“Wow, that’s—”

If it weren’t for everything I’ve seen in the last twenty-four hours, I would think she’s lying. I shake my head, realizing that everything I thought I knew—about myth, about Medusa, about whether monsters might really exist—is wrong.

“How—” I begin again. I have to swallow before I can finish. “How did that happen?” I ask. “How did the real story get so twisted?”

“Ursula, my mentor, says it began with Athena’s jealousy.” Gretchen shrugs as if it’s no big deal. “She thought Medusa seduced Poseidon, and she wanted revenge.”

More mythology lessons resurface. “That’s why she helped Perseus kill Medusa, right?”

Gretchen nods, and I feel a little surge of pride.

“Ever since her assassination it’s been up to her descendants to keep the monster population in check,” she explains. “Something I’ve been doing for the past four years.”

Four years? That’s a long time, a quarter of my life. I wonder if it’s been a quarter of her life too. As much as I might want to believe she’s my long-lost sister, just because we look alike and see the same monsters doesn’t necessarily make it true.

But I have to ask.

“And do you think . . . ?” I can’t bring myself to finish the question.

In truth, I’m not sure what I want the answer to be. There are pros and cons either way. If it’s yes, then I’m some kind of mythological monster hunter, destined to fight the disgusting creatures I’ve been seeing for two days. If it’s no, then Gretchen isn’t my twin and that empty spot in my heart stays wretchedly empty.

“That you’re one too?” she finishes for me. “I guess it’s possible.”

As I look at the girl who might be my sister, I realize the cons don’t matter. Blood matters. Family matters.

“I’m adopted,” I blurt, suddenly wanting everything to be true. Needing it to be true, needing Gretchen to be my real flesh and blood, even knowing what that means. As much as I love Mom and Dad and Thane, we don’t share any genes. It’s not the same. “I don’t know anything about my birth parents.”

Gretchen hesitates, freezing like a statue. I try to tune in, to sense some kind of twin connection. But she’s like a brick wall. Finally, after a long exhale, she says, “I was adopted too.”

There’s something in her tone, in her use of the past tense about her adoption, that makes me think that she wasn’t quite as lucky as I have been. I wouldn’t trade my mom and dad for anyone. I know things could be so much worse, that other kids wind up in awful homes all the time.

My heart goes out to her.

“Are you sixteen?” I ask, knowing this is the only way to be anything close to certain right now. It’s a very Parent Trap moment, only without the summer camp and the prank war. When she nods, I say, “My birthday is July thirtieth.”

I hold my breath, waiting. Hoping.

It feels like a lifetime before she says, “Mine too.”

My mind reels. Literally reels. I’ve always wondered about my birth parents, imagining what they might look like or what kind of people they are. Where did I get my silver eyes and my crooked pinky fingers? I used to spend hours at the mirror, studying every little detail and wondering where it came from. The identity of my birth parents has never been something I desperately needed to know, though. Mom and Dad are my parents in every way that counts. Maybe by the time I turn eighteen and can get access to my records, I’ll be ready to investigate.

But now, finding out that not only am I a descendant of some mythological guardian, but I also have a sister. A twin sister. It’s a little—

“I think I need to sit down,” I say, feeling a little bit lightheaded.

Gretchen pushes away from the counter. “Let’s go to the library. You can sit and I’ll try calling Ursula.” She leads the way into the room lined on three walls with books and binders. “There is some serious weird going on lately, and she might know why.”

She yanks open the sliding glass balcony door, and I suck in a breath of salty night air as I drop into a chair at the conference table.

“Weird how?” I ask.

“Like three monsters showing up in one night.” She drops into the desk chair and spins around once.

“That doesn’t usually happen?”