My great-aunt Bertha has loads of energy, and a friendly manner, and Alzheimer’s. She has an extraordinarily eventful life. In a typical week, she is visited by social workers, swindlers and the police, who smash down her door each time she’s locked out. Bertha’s not bothered. She’s like a dope head: give her a biscuit, she’s happy. And she forgets everything anyway. But she worries the hell out of my mum, who spends hours every day phoning, visiting and trying to coax her aunt into an old people’s home where she’ll be safe.

Monday, she finally manages it. Mum takes Bertha to Oak Fields, at the end of my street. I join them for lunch. Bertha’s on terrific form. She has just finished a dance class, and is sitting among some unlikely hoofers. “This is my friend, from the old days,” she says, introducing a 100-year-old woman, who speaks Spanish. “And you know my husband,” says Bertha, introducing me. “Hello,” I say, “I think we met at our wedding.” We take Bertha up to her room. “Look,” I tell her. “It’s the same hotel room we stayed in on our honeymoon.” “Oh yes!” says Bertha. “Wasn’t it fun?” I leave, lest I’m expected to re-enact it.

Over the next few days, thoughts of great-aunt Bertha bring a sharp stab of shame, but to be honest, almost everything does that — my undug allotment, my writing, and most relationships. We live in a controlled world, where you’re expected to be polite and professional at all times, but I’ve got nastiness in me, and it’s like wee in the bath — sometimes it just comes out. And this week is a particular strain. I’m tormented by a colleague who upbraids me for being rude, even when I’m not talking to her. By the end of it, I’m feeling as guilty as a dog who’s eaten a shoe.

Saturday, 6pm. I hurry to Bertha’s and find her in the Alzheimer’s lounge with two old men. We drink tea. We sing along to the TV. Then one man holds my hand. Is he making a pass? Who cares? It’s calming. He turns to me. “There’s a hole right through the wall,” he says. “And a tunnel! Coast to coast, it goes! Coast to coast, hoo hoo! I’m Raymond. You can call me Major!” Then he leaves, Bertha follows, and the other man starts up.

“You like women?” he says, his eyes sparkling with excitement. “I do!” I say. I’m curious to know where this is going and, for the first time in ages, I know it doesn’t matter what I say. He tells an absolutely filthy joke, and I laugh immoderately. Then Bertha returns, and we all watch a programme about Handel.

Oak Fields is wonderfully soothing. It’s my new favourite place. I’m there until 11pm. In the end, the nurse has to send me home.

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