It's Saturday afternoon and my friend Ella has toothache.

"It's awful," she shivers. "I've been on painkillers for weeks. And it's getting worse, I just know it is." She puts her hand to her cheek, shuts her eyes dramatically.

"Why don't you go to the dentist?" Silly question; I brace myself for the answer. Ella's reasons are legendary, enchanting. Homeric justifications for everything she does and does not do.

She blinks, pleats and unpleats her mauve chenille scarf thoughtfully. I wait. "Don't laugh," she says. "But I think I'm getting a phobia" - sniffing the air as if phobias were transported, plague-like, on invisible spores. "I think I'm turning into a dental phobic."

I do laugh, I can't help it. "Since when?"

"I don't know," she frowns, biting her lip. "It's been coming on gradually, over weeks or months. Since this tooth started giving me trouble, in fact. The more I think about it, the more certain I am."

"Ella," I tell her, because, let's face it, she's begging to be told, "you can't afford a phobia about this. Dentists hurt like hell, but not as much as persistent toothache."

"I know. You make it sound so simple," she sighs. "I'm so hopeless."

We drink our lemon balm tea in silence, relishing the temporary sanctuary of the child-free room, the hypnotic hum of the fridge. The table's a moonscape of hardened Weetabix, and four Cox's apples are wrinkling in a bowl. Through the kitchen window, trees darken, silhouetting themselves against a white, wintry sky.

Raphael comes in dressed as Troy Tempest, but with a pair of navy blue knickers pulled over his head instead of a hat. Dried snot is caked in glassy webs on his big, babyish forehead. "When is it Christmas?" he asks, lips bright with saliva.

"Not just yet."

"I'm hungry, but not for scrambled eggs." He pulls open the fridge door and stands there looking. I close it, steer him away, pour Ella more tea.

"I read about a dentist in a colour supplement," she continues, "who specialises in treating phobics."

"Well, could you go to him?" I try to rub Raphael's forehead with a damp flannel, but he buckles his legs, collapsing away under me.

"He was somewhere miles away. And it said he makes a point of never treating on the first visit." Ella clasps her tea-cup with immaculate fingernails. "And you see I would absolutely have to be treated on the first visit. I couldn't bear the angst of waiting."

At 4.30pm, she leaves, and Raphael and I go to the health-food shop for some bread. It's getting dark, the air is sharp, crystal cold. "No bread, sorry, end of the day," beams the woman, soft brown hair and soft brown voice. "Try the baker's over the road."

"Rai-sins," moans Raphael, knees giving way again.

"Okay, okay." I buy a packet. He grabs them with addict's fervour, scowling at the woman as she shuts the till.

"Bye now," she says with organic sweetness. In the street, people walk briskly in the blue light, a moped putters outside the pizza delivery shop. Someone shouts at a dog.

All that's left at the bakery is lardy cake and poorly looking sausage rolls. Two women in nylon gingham overalls mop the formica counter with cloths. "Sorry, love. We're closing - haven't got our lottery tickets yet."

Craving caffeine, I lure the Raisin Monster into Cafe Rouge. Subdued grown-ups eye one another against walls the colour of cold custard. We order a cappuccino and a pineapple juice. The pineapple juice comes with a black straw which pleases the Monster. "A Batman straw," he observes.

Back home, the air's bright yellow, fractious, and the stair carpet smells unaccountably of pee. I hear myself start to shout at the children. Chloe has tied Jacob's judo belt to the bannisters and is swinging from it. "You forgot the bread," accuses Jonathan.

"I did not forget!" I scream. A cat runs for the flap.

"I hope you haven't had caffeine?"

"Why should I have had caffeine? And why shouldn't I anyway?"

"You've had caffeine," he says grimly.

We bathe the children and read a chapter of Clever Polly and The Stupid Wolf. I identify with the Wolf. I, too, would like to eat someone.

Afterwards, Chloe chats about the nursery nativity play, in which she is to be the Angel Gabriel and Raphael a sheep. "I bring important news," she says, "But Raph just lies on the ground."

"And are you going to be a black sheep or a white sheep?" I ask Raphael, anxious to bestow importance on his role.

"A Batman sheep."

"If people didn't die," says Chloe, as I tuck them all into bed, "the air would just fill up with everyone and we wouldn't be able to breathe." I pause by the bunk ladder, struck by the virtual truth of this idea.

"You can get yourself frozen," Jacob shouts from his room next door, "so you don't die."

Chloe tucks my old Sindy doll - with her demure, pert, Sixties breasts - under a nylon doll's bedspread. "Well, how would I breathe if the air was full up with frozen people?" she yells back.

Coming downstairs, I stop by the dark landing window. A pointy crescent moon hangs poised over lit-up London and, just for a second, the air's thick with frozen bodies - a planet suffocating under the locust smog of its own technology.

If I weren't so tired, I could almost get up the energy to have a phobia about it.