The door opens hard against a security chain. I see one eye and a fringe of teenage hair.

"Are you Emily Martinez?"

No answer.

"Is your mum home?"

"No."

"What about your dad?"

She glances past me. "He'll be here soon."

"It's you I came to see, Emily."

She blinks at me. "I'm not allowed to let strangers inside the house."

"That's very wise. Maybe we could just talk here. You could stay in there and I'll stay out here."

She pushes back her fringe and I can see both her eyes and the braces on her teeth.

"You weren't at school today."

"I wasn't feeling very well."

"I talked to Miss McCrudden. She said you miss quite a lot of school."

Emily shrugs. She has a small neat nose, but carries weight beneath her chin.

At that moment a Black Lexus pulls into the driveway and a middle-aged man gets out, flipping the keys back and forth over his knuckles. Early-forties, tall and fine-featured, he looks like he's just stepped off a movie set, dressed in sharply pressed khakis and a business shirt. His curly hair is tipped with blond.

He mounts the stairs two at a time. Smiles. Open as a sunny day.

"This looks like good timing. We weren't expecting visitors."

He shakes my hand. Emily unhooks the chain and opens the door. Mr. Martinez hands her his briefcase and coat.

"I'm sorry, I should have called ahead," I explain. "I'm a.s.sisting the police in an investigation."

"Is this about Natasha and Piper?"

"What makes you a.s.sume that?"

He looks at Emily. "What else would it be?"

"I was hoping to talk to Emily."

"Oh, I see, well, Em's been off school today. She had one of her dizzy spells this morning." He puts an arm around her shoulders. "Are you feeling better, honey?"

She nods.

He continues, "She's already given the police three statements."

"Yes, but I'm looking at these things differently. It won't take long."

Mr. Martinez glances at Emily. "What do you think?"

She nods.

"Right, let's get inside. It's cold out here. Put the kettle on, Em?"

The lounge is a long narrow room with high ceilings and expensive furniture and paintings. The armchairs have the carved wooden legs of animals, as if they lead secret lives when everyone else is asleep.

Emily has gone to the kitchen. Phillip Martinez lights the gas fire and fluffs up cushions on the sofa. He has a smooth, almost feminine face with pale, barely existent eyebrows.

"This whole thing has been a terrible business-young girls running away. Not knowing what happened. It makes you wonder..."

"About what?" I ask.

"Excuse me?"

"What does it make you wonder about?"

"Their families." He makes it sound so obvious. "If things at home had been fine, they wouldn't have run away."

"What if they were kidnapped?"

"Well, that changes everything." He studies me for a moment. My left arm trembles.

"What stage?"

"I beg your pardon?"

"Your Parkinson's-what stage?"

"One."

"How long?"

"Eight years."

"It's slow-you're lucky."

"That's how I try to look at it."

"It's not really my field."

"Your field?"

"I'm a research scientist. I work at the Biomedical Sciences Department at the university. We do a lot of gene therapy research into things like diabetes, Alzheimer's and muscular dystrophy. Parkinson's is one area. Some of my colleagues are doing some important research. You should come and have a look. I could organize a tour."

"Thank you."

"That's one of the reasons Emily is quite wary of strangers."

"I don't understand."

"We use animals in our testing. Chimps mainly. There were problems during construction of the lab. Protests. Fire-bombings. Threats."

"Were you threatened?"

"My last car had acid poured over it and you should see some of the letters I received. I've taught Emily to be vigilant."

"I hope I didn't frighten her."

"Oh, she's fine. Highly strung. A bit like her mother."

Emily reappears. She's carrying a tray with a teapot and cups. Mr. Martinez takes it from her.

"I'm going to leave you two alone. I have emails to answer. I'll just be upstairs." He turns to Emily. "Honey, if you know something that could help, you tell him."

Emily nods and listens to her father climbing the stairs, following his progress, picturing him moving steadily through the house. Higher. Further away. Satisfied, she smoothes her dress over her thighs and sits on the edge of the sofa, toying with one sleeve of her jumper. Cautious and tense, she has a defeated expectancy about her, as though at any moment she expects to be admonished.

I've read her statements. Emily's story hasn't changed. But I know from experience how perceptions alter over time. I start gently, asking her about Piper and Natasha; how they met, what they did together.

She chews the skin around her thumbnail and occasionally nods and shakes her head. She doesn't want to talk to me and I don't have the codes to unlock her defenses-the mysterious combination of trust and shared experience that causes a teenage girl to prattle non-stop to her friends, but stop immediately when an adult walks into the room. If I knew the numbers, I could talk to my own teenage daughter.

"Do you have secrets, Emily?"

"What do you mean?"

"You understand what secrets are?"

She nods nervously.

"We all have them. Secret hiding places, secret crushes, secret regrets. We have faces that we don't show other people, only our friends."

Emily is staring at me with the dull frowning air of an amnesiac.

I try again. "Why did you want to run away?"

She shrugs.

"You must have had a reason. I know Natasha had some problems at school-what about you?"

"No."

"At home then?"

She hesitates and glances at the stairs, worried that her father might be listening.

"My mum had been sick. She had a breakdown."

"Where is your mum now?"

"She lives in a hostel in London. She's getting better."

"That's good."

Emily tugs at the hem of her tartan skirt. She hasn't touched her tea.

"Whose idea was it to run away?"

"Tash's."

"Where were you going to go?"

Her shoulders rise and fall.

"You must have imagined a new life."

"Yes."

"You didn't like this one?"

Again she looks at the stairs. "It was just talk at first. I didn't think we'd actually do it-not for real. It was exciting... something different... but then..."

"Then what?"

"Tash got serious."

"Why?"

"It was after the night Aiden Foster ran down Callum Loach. We made a sort of pact because things were so s.h.i.tty at school and at home."

"Why were things bad at home?"

Emily raises her eyes to the ceiling.

"Your parents were divorcing."

She nods.

"Tash sort of lost interest in the idea but then she got into trouble at school and Miss Jacobson said she couldn't come back after the holidays. Tash didn't tell her folks. She was going to run away before they found out."

"What happened on the night of the Bingham festival?"