‘Sugared flowers take hours to dry. If you didn’t plan to kill Marcus until after you killed Clementine, how did you have time to dump the body and the car and make a poisonous sugared flower, before dinner?’ Rosalind asked.

‘And you needed us to be on the steps to see you driving away as Clementine,’ Caro pointed out. ‘How could you make sure that we were watching? If it hadn’t been for the stolen magnifying glass – which we know you didn’t steal – Marcus would have announced the winner and people would have been getting on buses. One more car leaving wouldn’t have been noticed.’

They both already knew the answer to their questions, Posy realised. But it wasn’t until Isobel spoke that Posy realised she did too.

‘Juliette. You shouldn’t say any more.’ Isobel’s words were sharp, cold. Maybe she was disapproving of her granddaughter’s murderous actions, but Posy didn’t think so. ‘We’ll call the family lawyer. You mustn’t say anything else until he gets here.’

‘It was you,’ Posy said, hearing the amazement in her own voice. ‘You were her accomplice. You helped her move the body – she’d never have managed that herself, she’d have needed a second person, we always knew that.’ Even when she’d argued the case with the other Dahlias, she’d never really thought that smiling, composed, hostess extraordinaire Isobel could have been behind the murders. That definitely breeched etiquette rules. ‘Then she met you at the Gate House after to plan how you were going to kill Marcus, too.’

‘Don’t be ridiculous,’ Isobel snapped.

‘I don’t think it’s so ridiculous, Mrs Davenport.’ DCI Larch held up a mobile phone that Posy would bet once belonged to Clementine. ‘We did search the rooms as it happens. And we found this in yours. Now, I think you and your granddaughter should both come with me. Don’t you?’

‘Isobel.’ Hugh put a hand against the wall behind him for support, his face grey. ‘You didn’t. How could you?’

The last vestiges of Isobel’s mask of civility vanished. ‘What? Are you worried about your precious family reputation? I wouldn’t fret. We’re not blood after all, are we?’

Wrenching away from the policeman who tried to take her arm, she stalked across the room towards her husband. The others, Posy noticed, shrank from her as she passed.

‘I gave you everything – I was the perfect society wife you needed, the one Rosalind could never have been. I worked all these years to be what you wanted me to be. And all I asked in return was security, for me and my girls. And you were going to take that away.’