That night at the dinner table, Billie is especially quiet. Usually she and Noah joke around so much it drives their parents mad, but tonight nothing seems to make her laugh.

Even when her little brother sings a funny song and tips his bowl of peas over his head, Billie just stares down at her plate, pushing her fork around.

‘What’s the matter, Billie?’ her dad asks as he cleans up the mess. ‘You seemed so happy this morning. Is something wrong?’

Billie shrugs and jabs at a pea with the end of her fork. ‘It’s nothing,’ she says.

The truth is that she feels silly for being so grumpy. It’s just that the Secret Mystery Club was her idea. And she wasn’t even able to solve their first real mystery.

Noah slips down from the table and trots towards Billie. ‘Here, Bee-bee!’ he says softly, calling her by the nickname he has given her. He takes her hand and slips something into it.

Billie looks down at what Noah has given her. It is his favourite red car.

‘Thanks, Noah,’ Billie says, finally smiling. She kisses him on his soft brown hair. Noah can be the most annoying little brother in the world, but he can also be the best.

‘Come on!’ she says, hoisting him into her arms. ‘Let’s play cars.’

‘Cars! Cars!’ Noah shouts happily.

‘Come back in twenty minutes,’ Billie’s dad says, smiling. ‘I just have to make a quick phone call to Alex’s dad. He has a drill I need to borrow. Then I’ll make dessert.’

‘Can I have banana and ice-cream with sprinkles?’ Billie asks.

‘You bet!’ says Billie’s dad.

‘Thanks, Dad,’ Billie says. Banana and ice-cream with sprinkles will definitely cheer her up!