Dahlia would say that was a tell. A sign of a lie – or at least an omission.

‘What about?’ Caro pressed.

A muscle jumped in Posy’s jaw. ‘The curse on the movie. I don’t think it’s going to be a problem anymore. But he also confirmed that Marcus was behind the photos I was sent.’

There was a story there, and Caro wanted to hear it. But before she could ask for more details, Rosalind said, ‘Next course.’

Which brought them, inexorably, to the coffee and mints.

‘The book has the poison in the coffee cup,’ Posy confirmed. ‘They had wrapped mints on the saucers, just as we did, and coffee poured at the table. Dahlia reasons that the poison must have already been in the cup as a powder, before the coffee was poured in.’ She shut the book. ‘Except Marcus didn’t drink coffee, did he? He drank that foul camomile and ginger stuff. He made a big deal about it at lunch. I’d almost forgotten. But when I sniffed his cup after he, well, afterwards, it wasn’t coffee. It was tea.’

Now that sent Caro’s investigative brain whirring. ‘What does the script say? Anything about coffee, or the mints?’

Rosalind studied the script. ‘The stage directions mention the mints, the coffee, the sugared flowers—’

‘They’re not in the book,’ Posy blurted. ‘The sugared flowers. They’re not in the book.’

‘Are you sure?’ Caro asked, swinging round to stare at her. ‘They’re a new addition?’

Posy nodded. ‘Definitely. Libby must have added them in.’ She grabbed the script from Rosalind and flipped through the later pages, comparing it to the paperback in her hand. ‘And in the film, the poison isn’t in the coffee.’

Caro knew what she was going to say next before she said it. ‘It’s in the sugared flowers,’ she said, in sync with Rosalind, who’d followed the same train of thought.

‘Not in them,’ Posy corrected. ‘Every saucer has a sugared violet – except for the victim’s. They get a sugared monkshood flower – aconite. Ridiculously poisonous, and acts almost instantaneously.’

‘Someone switched Marcus’s flower for a poisonous one. And they’d know which cup and saucer was his because he had tea not coffee.’ The implications of that were huge, Caro realised.

‘So it could be done before the teas and coffees were served,’ Rosalind observed. ‘The cups weren’t on the dining table from the start – not enough space with eleven courses, I suppose. They were on the long table by the French windows, I think.’

‘Anyone in the room could have switched his flower then,’ Posy said. ‘When the serving staff brought Marcus’s cup over, it already had the teabag in – I was sitting next to him, remember? They gave him a little pot of hot water to go with it.’