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.’
‘I’ll ring Gareth,’ said Alice, getting to her feet. ‘He can bring some new locks home with him.’
‘Very wise,’ agreed Rushton. ‘But just hold on a sec, lass. I’m afraid that’s not all. You should probably sit down.’
Alice looked at the kitchen door. ‘I really need to check on the kids,’ she said.
‘Evi’s with them,’ Harry reminded her, wondering if