Grace brings home a friend. “Let’s run up,” she says. “Before Cassady sees us.” They sprint upstairs. They push beds against the door. They pile on armchairs. It’s a barrier that would stop a speeding car.

Cassady is four. She notices if peas are touching the ketchup. She’s definitely noticed the huge anti-Cassady barricade. She’s about to go off like a bomb. I must include her in the girls’ game. But I can't say, “Stop being rude. Let Cassady play.” That would be like giving Cassady to them as a punishment. I need to sell them the idea.

“It’s good that you’ve blocked the door,” I shout. “We’re playing a brilliant Cinderella game, and this is the castle, but we can’t get in. I am the Magic Horse, and Cassady is going to jump on me.”

They come straight out. I couldn’t have emptied the room faster if I’d used tear gas. “We’ll play,” they say. “Right,” says Cassady, instantly taking control. “I am Cinderella.” She’s giving herself the lead role. “You are the ugly sisters. Daddy, you are the wicked stepmother.”

“Great,” I say. I put on the wig.

“Nooo!” she shrieks. “You are the prince.”

“Perhaps I’m the prince,” I suggest, “disguised as the stepmother.” I’m pleased with this. I feel I’ve invented an original twist.

Cassady is staring at me. She is disgusted at the notion of a cross-dressing regent. She reasons that I have presumed to rewrite Cinderella, the most sacred of all texts. She’d be within her rights to send in the tanks.

“You are the prince,” she shouts, suddenly hurling herself to the floor and weeping.

“Cinderella,” I ask, “has it all gone wrong?” I’m trying to empathise.

“Aaagh!” she bawls, kicking her feet. “It’s all gone wrong.” The other girls are watching me. I don’t blame them for not playing with Cassady. I’m not wild about it myself. I’m yearning for peace quite badly. I do the only thing I can. “Girls,” I say, “who wants to watch telly?”

We watch some In the Night Garden, which calms us like Rohypnol. Then Grace whispers to her friend: “Let’s get upstairs. Quick!” And I pretend I haven’t heard.

Cassady is distracted by a big stone. “Now come on, Daddy,” she says, turning off the television ominously. “We’re playing March of the Penguins.”

Oh, lord. The last role-play didn’t get past the casting. But I’m curious.

“How do you play March of the Penguins?” I ask.

She puts the stone on her feet.

She waddles over, and tips it onto my shoes. Then we join wings, and rub beaks. It’s an outstanding precis of the film. It’s sublime, affectionate and completely wordless.