‘The point is, you had a woman who could steal your inheritance, and now a man who knew that secret – and would blackmail you or blow the scandal wide open. Either way, you had to keep him quiet.’ Caro started pacing again. ‘You all knew, because it had been planned by Isobel, that the first night banquet was a replica of the one in the new film of The Lady Detective. The script was sitting up here on Hugh’s desk, so you knew about the sugared flowers, too – even though they weren’t in the original book. And from here, you can see the blooming monkshood in the Murder Spiral, the same dark blue as the sugared violets that were drying downstairs in the kitchen. It’s easy to see how the plan came together.’

‘And the spilled sugar in the Gate House confirmed our suspicions,’ Rosalind added. ‘Obviously you made your own, deadly version – carefully, I imagine – and added it to Marcus’s saucer at the last moment. He was eating in a room full of people he was either blackmailing, taunting, or whose secrets he knew. There were plenty of suspects for you to hide behind – and with aconite being such a fast-acting poison, plus his well-known medical history, it was likely his death would be ascribed to a heart attack, like it would have been in the past.’

‘Our medical teams are rather more accomplished now than they were in the thirties, though,’ Larch drawled from the doorway.

‘But the murder was spotted,’ Caro continued, ignoring Larch’s interruption. ‘And the rainstorm the next night meant that Clementine’s body was found, too. And when we started to investigate her death, that was when things started to fall into place.’

Rosalind took up the narrative again. ‘The part that threw us off for the longest time was the phone calls. Clementine called Hugh to ask to borrow a car to leave for a family emergency – an emergency her family have no knowledge of, incidentally. And then she called Marcus and left him a voicemail explaining the same thing, later that evening.’

‘Except Clementine was already dead by the late afternoon,’ DCI Larch added. ‘According to my guy.’

Rosalind nodded. ‘I’d guessed as much. You see, we posited that Clementine pretended to leave Aldermere, but then drove around the track on the other side of the river, left the car and crossed the bridge to meet her killer at the Boat House.’

‘But Felicity told us she’d seen Clementine crossing the lawn to the Gate House later that afternoon,’ Caro put in. ‘And when we searched the place last night, we found the clothes she’d been wearing earlier that day, but no other sign of her except that spilled sugar.’