James realised then why the ceiling was at such a steep angle – they were standing beneath the stairs that were located in the living room.

‘So, what’s so unusual about this?’ he asked.

The officer pointed to a spot on the wall and shone the torch at it. James saw a small, dark circle about an inch in diameter.

‘This, Inspector, is a hidden peephole. It’s made of brass and is similar to those used in front doors. And by looking through it you can see what’s going on in both the living room and kitchen. You just have to stand on this stool.’

He invited James to step forward and check it out. James stepped on the stool and put his eye up against the device to peer through it. What he saw surprised him.

The peephole gave an elevated wide-angle view that was slightly magnified. He could see Dr Flint and the SOCOs working away, unaware that he was looking down on them. But not only that. He could also hear them clearly as well.

‘Believe it or not it’s almost impossible to spot it from the inside,’ the officer said. ‘I checked, and even though I knew what I was looking for, it took me a while to locate it.’

‘And why is that?’ James asked.

‘The wallpaper under the stairs has a garish raindrop design. The peephole has been carefully placed in one of the drops.’

‘Bloody hell.’

‘Now step back down, Inspector, but be careful where you place your shoes.’

When James had done as he was asked, the officer shone the torch beam at the floor.

‘I also spotted these,’ he said. ‘They’re breadcrumbs, and they’re just days old at the most. Which tells me that someone has been in here recently to spy on the family.’

James felt his spine stiffen. ‘This is crazy. And there was me thinking that this case couldn’t possibly throw up any more surprises.’

‘Well actually, there’s more,’ the officer said. ‘Come and see.’

James followed him out of the cubbyhole and the officer shone his torch at the stain on the stairs next to the evidence marker as they passed it.

‘I’m pretty certain that’s blood and it hasn’t been there long. We’ll scrape if off in the hope that we can extract some DNA. But at this moment there’s no way of telling if it belonged to any of our three victims.’

By now James’s mind was leaping all over the place and adrenaline was pumping through his veins.

‘Keep up the good work, officer, and turn the cubbyhole and the cellar inside out. My gut is telling me that piecing this all together isn’t going to be easy,’ he said.

DC Abbott was waiting for him at the bottom of the cellar steps.

‘So, what do you make of it, guv?’ she said.