Crawfie had heard enough. She got up and brushed the grass from her skirt. ‘Lilibet, Margaret, who’s for a game of catch?’

The detectives glanced at each other quickly, hoping she hadn’t overheard anything. Both scrabbled for the tennis ball. ‘Come on, ladies,’ Williams shouted, ‘who’s going to play catch?’

The girls darted and shrieked and tumbled as Williams threw the ball high and let the Princesses run for it.

Crawfie, watching them, began to fold the blankets and collect up the greaseproof-paper wrappings that the sandwiches had come in. She emptied the beakers onto the grass and tucked them around the napkins, then stowed everything between the five bicycle baskets.

She was working as an automaton, still shocked by what she had heard. Her body did what it knew it had to do, while her brain was filled with the disgusting conversation she had listened to. She only knew the theory of the sexual act, and that rather patchily, but had always imagined it as loving, precious and private. She had always liked Mr Brown and Mr Williams, but what sort of men would idly discuss it and laugh?

She thought of George and the unformed fantasies she had about him. And why hadn’t he written for so long? Had she done something wrong? Perhaps he was ill, or something terrible had happened.

She made up her mind to write to him tonight once all her work was finished. This thought alone made her feel a little better.

Above her, a blanket of clouds was moving over the sun, and she shivered in the light breeze.

‘Ladies,’ she called. ‘Time to go home, before it rains.’

‘Can we cycle down the Long Walk and find conkers?’ Lilibet asked. ‘Please?’

Crawfie checked the sky and her watch. ‘All right, but just for ten minutes or they’ll be wondering where we are.’

They got back to Royal Lodge just as the rain was starting. Williams and Brown took charge of the bikes and wheeled them back to the stables and Crawfie was relieved to see them go.

The Duchess was waiting for them in the hall. ‘My darlings.’ She hugged them. ‘Have you been good girls for Crawfie?’

They looked at Crawfie for the answer. ‘Have we?’

She smiled. ‘Yes. Very good.’

‘Excellent.’ The Duchess turned back to her daughters. ‘Guess who is coming to dinner tonight?’

Margaret was thinking. ‘Hmm.’

Lilibet put her hand up. ‘I know.’

Margaret, desperate to answer first, started jumping up and down. ‘I know! It’s Peter Pan and Wendy.’

Lilibet frowned. ‘You’re being silly.’

‘Now, now, darlings.’ The Duchess intervened. ‘It’s Uncle David. And he’s bringing his friend, Mrs Simpson.’ She looked at Crawfie. ‘Would you ask Alah to bring them downstairs after their dinner? At quarter past seven, just for a few minutes. In their nightclothes will be fine.’

‘Yes, ma’am.’

Up in the nursery, Alah was fighting a summer cold. She was wrapped up by the fire, while Bobo made her warm lemon and honey.