Since he’s waited this long to call, I hope that means he thinks I got lost on the way to bathroom or something.

With a deep breath, I punch the answer button. “Hey,” I say, trying to sound un–freaked out. “What’s up?”

“Are you ready to go?”

Whew. He must not have seen me carried away like a sack of apples.

“Am I ready to go?” I ask to buy time.

“It’s not a trick question.”

Cover story, Grace. Come on, you’re a smart girl. You can do this. “Um, I—er, ran into a new friend.”

“New friend?”

“From school.” For the first time, I’m really thankful Thane and I are not at the same school. Otherwise he’d know I haven’t met a single person I could call a friend. “Yeah, she lives nearby and invited me over to watch movies.”

“You left?”

The heavy silence after his question tells me he’s angry. Rightfully so, since I bailed without telling him and can’t exactly share the real reason.

“Sorry,” I say, glancing up at the rusty door. I don’t have time to deal with Thane right now. Not when I have a mysterious, monster-fighting twin upstairs who has answers to my burning questions. “I should have told you first.”

“Grace—”

“Look, I gotta go,” I said, partly because I don’t want to risk answering any more questions, but also because my curiosity is killing me. I need to know what’s up with the monsters and why no one else can see them and who the lookalike girl is and a million other things. Thane will be waiting at home. I can only find my answers upstairs. “I’ll call home to let them know what’s up.”

I hang up before he can argue.

I allow myself a few seconds of rest against the railing before gathering the courage to call Mom. Before gathering the courage to lie to Mom. In the end, the call isn’t as stressful as I feared. I give her the story about running into a friend and going over to watch movies. After assuring her that my friend’s parents would bring me home before midnight, she lets me go without an interrogation. She’s probably thrilled to think I’ve made a friend.

“Little does she know,” I whisper, pocketing my phone and following my double up the stairs.

As I push open the squeaky door, I’m shocked to step into an entirely modern space. All the surfaces are gleaming black and white, polished metal, and shiny glass. The complete opposite of the dull beige exterior and the rusty metal garage area.

“Wow,” I can’t help but say to the expansive room.

It’s such a huge, open space. I sweep my gaze around the room, taking everything in. Directly in front of the door is what looks like a living room, with black leather sofas and armchairs around a metal-and-glass coffee table. Along the right wall is a trio of doors, maybe bedrooms and a bathroom, on either side of a flat panel TV the size of my bed. Across the living room is a glassed-in space lined with full bookshelves and with a giant conference table surrounded by chairs in the center and a computer workstation along one wall.

To my left is another door next to a black granite and stainless-steel kitchen and an equally sleek dining room.

Despite all the slick and shiny covering every surface, the thing that enthralls me is the far wall. Floor-to-ceiling windows, with sliding glass doors and a balcony beyond. Both the dining room and the library have unobstructed, picture-perfect views.

I make my way past the kitchen toward the balcony. I slide open the doors and step out into the chill air. The view of the Bay and the houses, boats, and other lights twinkling all around is breathtaking. I’m so caught up by the sights before me that I don’t hear my double walk up behind me.

“What’s your name?” she demands.

My heart jump-starts and I whirl around with a gasp, clutching my palm to my chest. “Omigosh, you scared me.”

She lifts her brows.

She’s pulled off the long-sleeved black tee she was wearing at the club and is now in a black tank top. One leg of her cargo pants is rolled up to the knee, and her ankle is wrapped in white gauze. She’s dabbing at the back of her neck with a cotton pad soaked in a blue liquid that smells like mouthwash.

“Grace,” I say, leaning back against the railing. “My name is Grace.”

“Grace what?”

“Whitfield,” I answer. “What’s your name?”

She turns away, walking back inside. I follow her through the living room and into a brightly lit bathroom, a little annoyed that she ignored my question. Twisted around with her back to the mirror, she’s trying to secure a second gauze bandage to the back of her neck.

“Here,” I offer. “Let me help.”

She gives me a skeptical look but doesn’t argue when I brush her hand aside and hold the bandage to her wound. As I tear off a piece of first aid tape, she mumbles, “Gretchen.”

“Gretchen?” I echo, securing a second piece of tape.

“Sharpe,” she says, almost reluctantly.

I release the bandage, and it seems like it’s going to stay in place. I step back and around to face Gretchen. With a smile, I say, “All patched up.”

She mutters a quiet “Thanks,” and then turns to put away the first aid supplies.

I would offer to help, but I have a feeling she’s not interested.

“So, Gretchen,” I say instead. “Wanna tell me what’s going on?”

She closes up the first aid box, slides it under the sink, and then leans back against the counter. It’s hard not to squirm as she scrutinizes me with eyes the same silvery gray as my own.

“That depends,” she says, crossing her arms over her chest. “How much do you know?”

I laugh. A big giant guffaw just bursts out, I can’t help it. It’s a slightly hysterical reaction to an extremely ridiculous question. “How much do I know?” I ask, still laughing. “I know that yesterday I started seeing monsters from Greek mythology come to life, and you look like my twin.”

She looks at me, like she’s waiting for me to say more. When I don’t, she asks, “That’s all?”

“To the syllable.”

“And before yesterday you never saw a monster?” She uncrosses her arms and tucks her hands into the back pockets of her black cargo pants.

“Not once.”

“What happened yesterday?” she asks.

“I told you,” I say, getting a little frustrated that she’s doing all of the asking and none of the answering. “I saw the minotaur in the dim sum parlor. And then I—”

“No, before that.” She shifts her weight to the other foot. “What was different about yesterday? What’s changed in your life recently?”

Well, there’s only been one really big change.

“We moved to San Francisco,” I say, using up the last of my patience. “Yesterday was my first day at the new school.”

“That explains it,” Gretchen says, as if now everything should be clear. “Monsters don’t get far from the city.”

Without another word she walks out of the bathroom, leaving me standing there like an idiot, facing my own reflection. That explains it? That doesn’t explain anything.

“Grrr,” I growl at the mirror.

I let myself get kidnapped by a stranger and then lied to my family about it. I at least deserve some answers in exchange. Obviously, she’s not going to give them to me. I have to go after them.

I stomp out of the bathroom.

“Look,” I say, finding her in the kitchen. “I want to know what’s going on. You obviously know a lot more than I do.”

“It would be hard not to,” Gretchen says, pulling an energy drink out of the giant silver fridge. “Want one?”

“No. I want answers.”

“Fine,” she says with a sigh. She pulls the tab on the energy drink and throws back half the can before continuing. “Here’s what I know. I’m a descendant of the Gorgon Medusa, and—”

“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.