‘Aren’t you big, Ronnie!’ she said, cuddling him and making him beam. But as Nina moved about the kitchen, putting out a plate of biscuits and sitting at the Formica table, she saw how much her mother had aged in the last six months. She was greyer, more stooped and uncertain, more defeated. Her brother had warned her, it had all come on so quickly. She was only sixty-three. Sixty-three! Unable to let her hands lie still, she kept smoothing her hair, her thighs, or rubbing her forearms, up and down, an incessant habit. Sometimes, when she remembered or Jared handed it to her, she squeezed a raspberry-pink stress ball with a nubby surface.

This was what Nina’s mother’s Alzheimer’s was like. It seemed less like an illness of forgetting than a bad case of anxiety. She had always been anxious, had always rubbed her forearms when she worried, but now it was as if the worrier was the only part of her left.

It had been three years since Helen was diagnosed with the disease. Until then, Nina knew almost nothing about Alzheimer’s. Working as a director, she’d made mini-documentaries for charities, short films about misfortunes that happened to other people. Blindness, for instance. Or having your life saved by the London Air Ambulance. For the macular blindness one, she used blurry and shadowed footage to mimic the progression of the illness. First a shot in which a mother adjusts her son’s school tie, then a later shot where she can’t.

In the Air Ambulance one, she filmed a road accident survivor. She took him back to the intersection and had him tell the story: how he was hit by a car while riding his bike, how the car ran him over, crushing his pelvis. Going over the footage later, she cut the part where the man cried, deciding to show him almost-crying instead. You had to hold something back, give the viewer room to feel. Her style played well with the British. They were crazy for stoicism, someone keeping it together. When she played a cut of the film, the reps from the client started crying. They hugged her and said they could not have been happier.

But Alzheimer’s had been a mystery. Slipping away from the gathering in the kitchen to look around the house, Nina saw evidence of her brother’s efforts and felt the familiar guilt. Thanks to him, the bathroom sported a new set of safety handles – plasticky, beige and sturdy; not very attractive. On the fridge door she had noticed instructions for the carers, a laminated mini-essay with the heading ‘A Typical Day’. Helen has two crumpets with honey for breakfast. There are crumpet bags in the freezer. If the left side of the toaster sticks, give it a jiggle…