“There’s a recording that I’d like to have analysed. I need you to authorise it for Forensics.”

“Is this for the Tranter twins abduction case?”

“Yes. It’s from the 999 call Lauren Tranter made from the hospital. Despite the doctors’ reports asserting that there was no intruder, the tape suggests that there was one.”

Thrupp rolled his eyes. “Oh, that. Haven’t we wasted enough time on that? The doors were locked, the nurse said there was no one there. Is the tape conclusive evidence? Good enough to contradict the statements of a senior midwife and a consultant psychiatrist?”

She couldn’t lie, not directly into his face. “Not exactly. But if we have it analysed—”

“OK. Do you have a suspect in mind?”

No, she did not. But she couldn’t say that. “Maybe it was Natasha Dowling.”

“Aha. Didn’t we just eliminate Natasha Dowling?”

“Yes, but I think there’s more to it. Perhaps she had an accomplice, we’ve not considered that. I came across this article, which may be of interest.” She handed over the photocopy from the Mail.

When Thrupp had read it, he snorted and handed it back. “Where did you get this from?”

“A journalist, if you must know.”

“Well,” said Thrupp, “let’s not start letting the hacks do our jobs for us, shall we? It never turns out well. That’s a coincidence. Nothing more. It was more than forty years ago.”

“Yes,” said Harper, folding the piece of paper and putting it back in her bag, “I thought that, too, at first. But perhaps it’s linked somehow. Perhaps the perp from that case is pulling the strings, getting Natasha to do her dirty work.” It sounded ridiculous, even to Harper.

“Seriously?”

“Well, it’s a theory.”

“It’s a stretch, is what it is.”

Harper tried again. “If it is Dowling on the tape then we can still charge her, with harassment. She followed Mrs Tranter, after all, we can prove that much. She’s been stalking Patrick for weeks. And, even if it’s not her voice, then we’ll have something on file to compare when we do find the perpetrator. The point is, it’s worth having it analysed, don’t you think?”

Thrupp gave her a long look. “What does the voice say, exactly?”

“It’s not entirely clear, but the voice makes threats of some kind. It needs cleaning up and investigating, firstly to see what the words actually are, then to see if the vocal patterns match.”

Thrupp made a sceptical face. “This case is about to be dropped, Jo, so the evidence trail needs to be truly rock solid. I mean, like, granite. If it’s just a fuzzy recording of nothing, and there’s no suspect in the frame, then I can’t justify it.”

“The case is being dropped? Why?”

Thrupp started counting on his fingers. “One. The babies are, in fact, no longer missing.”