Internally, however, she’d closed in on three main ones: a) an intruder had approached the house from the rear and had got inside that way, because Harry Hopkins had forgotten to lock up; or b) Harry Hopkins had gone outside himself, leaving the property by the back door and the back gate, and for some unknown reason had still not returned; or c) neither of those unpleasant alternatives had happened, and he was simply going about his everyday business, absent from home at this moment, again having neglected to lock up (and having left his hat and coat behind), and by pure coincidence had also been absent every time in the last three days when his daughter had phoned the house.

You wouldn’t earn a police commendation for working out which of those options seemed least likely.

Lucy stepped through into the back alley. ‘How often have you tried to contact your father in the last few days, Janet?’

The woman followed her out. ‘First it was every few hours, but then … I mean yesterday and last night, it was once every ten minutes.’

‘Is your father hard of hearing, by any chance?’

‘He wears a hearing aid, but no … he can hear when the phone’s ringing. He normally answers straight away.’

Lucy surveyed the alley. It was narrow, cobbled, and little more than a service passage running behind the row of houses. At present, it was clear of vehicles, or bins, or sacks of rubbish. On the other side, a high red-brick wall rose about ten feet, screening off the rest of the estate.

Lucy wasn’t comforted by this. A narrow backstreet hidden from view on one side.

She turned back to the gate – and stopped in her tracks. Like the house’s front door, the back gate had been painted a bright canary-yellow, but on the outside it had been spattered top to bottom with dried black trickle stains.

‘This is a bit of a mess, isn’t it?’ she said.

‘Oh.’ Janet Dawson looked genuinely surprised. ‘Dad’ll go mad if he sees that. He hates scruffiness.’

‘He’d scrub it off, would he? Even though it’s on the outside?’

‘Certainly. As soon as he saw it.’

Which likely means this has happened since he went missing, Lucy thought to herself. Or did it happen at the time he went missing?

She wondered what might have caused it. A vehicle travelling at speed would have kicked up ground water, spraying the gate, though not today of course; it was sunny today, unusually warm for mid-September. She glanced around. The cobblestones were bone-dry. Thinking about it, the last time they’d had proper rain – the sort that would leave proper puddles – was on Tuesday afternoon.

Three days ago.