He pointed at her bare foot. A clearly defined red mark ran across the top of it.

‘There’ll naturally be tissue damage from the fall, although she died instantly from a broken neck, but this looks, well . . .’ He stared at the thin, dark-red line.

Laker had been right in his suspicions, but there was something even more sinister. ‘I think I know exactly what that is, Doctor.’ She’d seen it before. A girl who’d been tied around the wrists. The cord had left a thin, red weal, just like the one across Nan Cutler’s foot.

Marie went up the stairs and took note of the position of the single red velour slipper. Then she knelt down a couple of stairs below and scanned the top step, as well as the wall on the other side of the lone slipper. She looked more closely at the top step, got her torch from her pocket and directed the light along the paintwork. There! One tiny hole.

She swung the beam across to the other side of the stairs and found a corresponding hole in the upright of the newel post. Two slim nails, or maybe even picture-hook pins, had been enough to secure a tripwire. Afterwards the killer had removed the wire and pins, but there was nothing to be done about the holes.

‘Simon, can you ring this in, please? We have a crime scene. I want the area sealed off and a log set up immediately.’

‘Murder?’ Dr Mason sounded incredulous. ‘Surely not?’

‘Tripwire, Doc, that’s what caused the welt on her foot. She steps forward, catches her foot on the wire and, leaving the slipper behind, lurches forward and down the stairs — with considerable impetus, I should think — hence the broken neck.’

‘I don’t understand,’ Dr Mason said. ‘Who would want to hurt Nan Cutler? She was just a harmless old lady.’

‘That’s for us detectives to figure out, Dr Mason,’ said Marie angrily. This was unforgivable. There was no room in the world for someone who could commit such a despicable act.

While she waited for Forensics and a uniformed team, Marie spent the next twenty minutes going over in her head the possible reasons for wanting Nan Cutler dead. A red-eyed Lizzie Coupland had brought tea for her and Simon, and they stood with their steaming mugs hypothesising over different possible scenarios. By the time the police vehicles were pulling up outside, they were still none the wiser. At least Simon had been able to assure Eric that he was definitely not to blame for Nan’s death.

Marie was surprised, given how early it was, to see the Home Office pathologist, Professor Rory Wilkinson, draw up in his battered lime green Citroën Dolly.

‘Well, well, well! DS Marie Evans, recently returned from the land of my fathers — I mean land of her fathers. And a good bore da to you.’

Marie grinned somewhat mischievously. ‘And cyfarchion i chi!’

‘Now don’t get smart with me, Evans. At least I managed good morning — give me some credit.’