“I don’t know, sir. How should I know?” But she did know, at least the essence of it; the desperation, the protective instinct that would be driving her on, twisted though it might be.

“Well, you saw her a couple of days ago, didn’t you? What was she like? Would she harm the babies, in your opinion?”

“I don’t think so.”

“OK. Maybe she’s not planning anything sinister. Let’s hope.”

“She might simply be hiding somewhere nearby. Should I head for the unit, to help the search?”

“Yes, do that. I think you’re right, we should go through the building and the grounds thoroughly before widening the search area.”

“You should put the helicopter on standby until we’ve completed. No point wasting resources if we think we might find her in a cupboard or something.”

“Good point.” Thrupp sounded very approving of her cost-saving suggestion. “One more thing. I can’t get hold of the husband—could you try him? I’ve left messages on his landline.”

“I’m at the Tranters’ now, actually, returning his mobile phone. I think I know why he hasn’t picked up his landline messages. I’ll make sure he does. And I’ll meet you at the unit as soon as possible.”

Harper typed one last message to Amy before she started the engine: Tell your boyfriend to listen to his messages.

She’d been driving for only a few minutes when her phone rang again. She hoped it was Thrupp, calling to say they’d found Lauren and the babies safe and well.

It was Gideon. She put him on speakerphone and continued to drive.

“What is it?”

“I did the analysis you asked for, on the phone call. I thought you’d like to know the results.”

She’d forgotten all about it. Yesterday she’d asked Gideon if he could compare the voices on the 999 call, to see if the intruder’s voice matched with a sample of Natasha’s that she’d retrieved from Patrick’s phone. It didn’t seem to matter now.

“Thanks, but we’ve had to drop that line of enquiry. I’ll still pay you for your time, of course.”

“I still think you’ll be interested.”

“Oh?”

“Firstly, there was no match with the suspect, the sample voice you provided.”

“Ah. Well, I would have been surprised if there was, at this point. I think we’re looking for someone older, maybe in their sixties …”

“In fact,” said Gideon, “there were only two distinct voice patterns on the whole recording.”

“Two?” said Harper. “What do you mean? There’s the operator, Lauren Tranter, and the suspect. That’s three.”

“Definitely only two,” said Gideon. “I checked again and again. There was one unique vocal pattern for the operator, and the only other one was …”