‘WHAT’S AN EMERGENCY PROTECTION ORDER?’ ASKED Harry.

‘It’s a court order,’ replied Hannah Wilson. ‘It allows children to be taken into care for their own protection. They’re effective immediately.’

Harry sat back down, moving his chair closer to Alice. She was sitting quite still; he might almost have thought she wasn’t listening, had it not been for the trembling in her fingers.

‘Have you discussed this with Dr Oliver?’ asked Harry. ‘As the family psychiatrist I’d have thought she’d be the obvious person to consult.’

‘Dr Oliver can submit a report, of course,’ replied Wilson. ‘I’m sure the magistrate will take it into account.’

Harry was about to respond – quite what he would have said, he hadn’t quite decided – when they heard footsteps coming down the stairs. They could hear Rushton’s distinctive voice, then the front door opening and closing. The footsteps turned in the direction of the kitchen then stopped.

‘This is something the family need to know,’ they heard Rushton say, in a voice that was low but firm. Then he came into the room, knocking on the door politely as he opened it. He was followed by DI Neasden and a female constable. Neasden didn’t look happy.

‘Sorry to interrupt, Mrs Fletcher,’ said Rushton. ‘Need a word, if I may.’

Alice seemed to be bracing herself for another blow. ‘OK,’ she said. ‘Do you need to see me alone?’

Rushton looked quickly round the table, avoiding Neasden’s eyes. ‘Oh, I think we’re all friends together,’ he said. ‘’Ow do, Hannah. You on your way out?’

‘Have you found something?’ asked Harry.

‘I think so,’ replied Rushton. ‘What time’s your husband home, Mrs Fletcher?’

Alice seemed to have lost her ability to think quickly. She glanced at her watch, then at Harry. ‘He said he’d be a couple of hours,’ she said after a moment. She turned to the kitchen clock on the wall behind her. ‘A site inspection he couldn’t get out of. He should be back any time now.’

‘Good,’ said Rushton. ‘And you might want to get a locksmith up here. See if these locks can’t be changed.’

‘What is it?’ asked Alice.

Rushton pulled out the chair Evi had just vacated and sat down. Behind him, DI Neasden, his lips pressed tightly together, leaned back against the tall kitchen cupboard. The constable remained by the door, softly closing it behind her.

‘You remember we found some footprints in the garden last night,’ began Rushton. ‘Our forensics people took casts of them.’ He turned to the man behind him. ‘Have you got it, Jove?’ he asked.

DI Neasden had been carrying a thin, blue plastic wallet. With obvious reluctance, he pulled a stiff sheet of A4 white paper from it and handed it to his boss. Rushton turned it to face Alice and Harry. It was a photograph of a footprint in mud.

‘We know the prints must have been left in the garden late last night,’ said Rushton, ‘because of all the rain you had up here. If they’d been left earlier in the evening, they’d have been washed away. So we know at least one person apart from your children was out there round about the time the wall came down.’

Hannah leaned forward to study the print.

‘We took several casts of footprints last night,’ said Rushton, ‘and a whole load of photographs, but this one is the most clear.’ He turned to Harry. ‘You remember me mentioning that the constable who was first on the scene was a bright lad?’

Harry nodded.

‘Brighter than I thought, it turns out,’ continued Rushton, ‘because he spotted this print, knew the rain would compromise it and put an upturned bucket over it until the crime team could get here. They were able to take some very good photographs and make a good cast.’

‘They’ve made a cast of this?’ asked Alice. ‘What with – plaster?’

‘Dental stone, I believe,’ answered Rushton. ‘A very tough, durable sort of plaster.’ He pointed to the footprint. ‘This here’s probably a size seven, maybe an eight,’ he said. ‘Not the most helpful to have, frankly, because it could be a tall woman or a small-footed man. You’re a size four, I understand, Mrs F?’

Alice nodded. ‘And Gareth’s a-’

‘A ten, yes, we know. We took casts of his prints as well. Matched them to the boots he was wearing when he went outside. These prints are quite different. Much cruder tread on them. Can you see?’ Rushton ran his finger around the outline of the print.

Harry leaned forward to get a better look. Horizontal ridges ran across the print. From the shadows on the photograph they looked deep, the sort of ridges you might see on a boot made for walking through deep mud.

‘Looks like a bog-standard wellington to me,’ he said. In the instep arch between sole and heel, he could just about make out an incomplete shape, maybe two-thirds of a gently rounded triangle. ‘Is that a manufacturer’s logo?’ he asked.

‘Yes, indeed,’ said Rushton. ‘And although it’s difficult to see, I’m told the letters immediately below it say “Made in France”. Shouldn’t be too difficult to track down the make and manufacturer.’

‘But you knew about the prints in the garden last night,’ said Alice. ‘Why have they suddenly become so-’

‘Ah,’ interrupted Rushton. ‘But last night we didn’t know about the matching one upstairs.’

‘Boss, we really shouldn’t be…’ said DI Neasden.

Rushton held up a hand to silence him. ‘There are three young children in this house,’ he said. ‘They need to know this.’

‘Excuse me,’ said Alice in a low voice. ‘Matching one upstairs?’

‘On the landing,’ said Neasden, with a resigned look at his boss. ‘Right outside your daughter’s room. I’m afraid whoever was in your garden last night was in your house first.’

Alice’s fingers rose to her face. It would have been difficult to say which had the least colour.

‘Yes, I know, lass,’ said Rushton. ‘Very upsetting, but it means we’re getting somewhere.’

‘I looked last night,’ said Alice, who didn’t seem to want to believe it. ‘I didn’t see any sign that anyone had-’

‘No, you wouldn’t,’ replied DI Neasden. ‘It’s what we call a latent print. Just about invisible to the naked eye and typically left by shoes that are quite clean.’

‘You see, lass, shoes pick up traces of whatever we walk on,’ said Rushton. ‘It’s called Locket’s Law or some such.’

‘Locard’s Exchange Principle,’ interrupted Neasden with the first smile Harry had seen on his face. ‘Every time two surfaces come into contact there’s potential for the exchange of physical materials. We carry away something of what we encounter, everywhere we go.’

‘Yeah, that’s it.’ Rushton nodded his head in his DI’s direction. ‘So, as I was saying, every time we walk on something – dust, mud, carpet and so on – tiny particles cling to the soles of our shoes and then when our shoes come into contact with a clean, dry surface, such as your floorboards upstairs, Mrs F, they leave a faint print behind. We find them – when I say we, I mean my clever lads and lasses – in the same way we find fingerprints. We dust with fingerprint powder and then lift the print with adhesive tape.’

‘Just the one print indoors?’ asked Harry. Rushton turned to the inspector for confirmation.

Neasden nodded. ‘We’re pretty certain there’s nothing else,’ he said. ‘I don’t doubt there could have been more last night, but there was a lot of coming and going in the house, even before we got here. Any others were probably lost. Doesn’t matter though. One’s enough.’

‘You OK, Alice?’ asked Harry.

Alice seemed to be getting some of her colour back. She nodded. ‘Actually, it’s a bit of a relief,’ she said. ‘It means Tom wasn’t lying.’ She was silent for a second. ‘He’s probably been telling the truth all along,’ she added.

Harry smiled at her and turned back to Rushton. ‘Can you trace the boot to its owner?’ he asked.

‘There’s a good chance.’ Rushton nodded. ‘We also, very conveniently, have a tiny gash in the right side of the sole, can you see?’ He tapped the side of the photograph with his right index finger. Harry saw a small indentation, only half a centimetre long. ‘Also, according to our lab, there are wear patterns visible. If we find the boot in question, we can prove the wearer was in your house and garden. Which, given the lack of any sign of a break-in, is why I brought up the subject of changing the locks. Perhaps think about a burglar alarm while you’re at it.’