It took the better part of three hours to drive through the heavy back-to-work traffic to where Ruby’s new mobile phone had pinged, a small canal wharf in the middle of nowhere, north of York. The data contained in the email stated that the phone had activated the nearby mast on Christmas Day. Therefore it was unlikely she was still going to be there, but at least it was a starting point.

At the wharf she parked and started walking toward the first narrowboat in the row, where she knocked on a window, three sharp raps. The afternoon was crisp and cold, frost laced on the edges of leaves, floating islands of ice on the river. The craft’s curtains were drawn, but she knocked once more anyway. There was no answer.

Jo glanced at the chimney of the next boat, from which she could see a curl of smoke escaping. When she knocked this time, a curtain twitched, and a few minutes later, a woman’s head appeared out of the hatch. Her white hair was messed up, and she had a face brown and wrinkled like a walnut. Clouds of steamy breath filled the space between them.

The woman squinted into the bright slanting sun. “Yes?”

“I’m from the police,” said Harper. “I’m looking for a young woman called Ruby. She’s traveling with a little girl called Leonie, about eighteen months to two years old.”

The woman climbed from the hatch onto the small deck where the tiller was, dragging a blanket that she wrapped around herself tightly in the cold. “No one here by that name, not that I know of.”

“What about a man called Sam Douglas?”

“Nessie? Yes, he was here.”

“Nessie?”

“That’s the boat,” said the woman.

“When was he here?”

“Day before yesterday. I saw her leave, oh, late morning, I’d say.”

“Her? I thought you said there wasn’t a woman?”

“I was talking about the boat.”

Joanna was holding it together, but the boat woman was starting to annoy her very much. At times like these, she did well to remember the tips she’d picked up at the two politeness training sessions she been obliged to attend as part of her CPD.

“Just to be clear,” said Joanna, “Sam Douglas, the man, not the boat. He plays the violin. Do you know him?”

“Yes. He built my kitchen. It’s very good. Are you looking for a handyman? Or a violinist?”

“No. I’m looking for a woman called Ruby and a little girl. I know they’ve been here, because we had a mobile phone alert from the area. You’re sure you haven’t seen them?”