It's Kathy, as always, who points out the problem: an ant is dancing on the tip of their baby's nose.

"Paul," she says, "do something. Do something, now!"

Jake sits on the kitchen floor, wearing only a nappy. He waves an arm and brushes the ant onto his leg, where it scuttles up a groove in his chubby thigh. Paul leans forward, pinches the ant and crushes it.

Paul hates ants. So does Kathy. Jake will too, when he's old enough.

"Do they bite?" Kathy says.

"I don't know," Paul says. "I don't think so."

In his peripheral vision, he sees Kathy shaking her head: this is not the life he promised her. He's working on that. He just needs a chance.

"No harm done," Paul says, and he shows her the ant pulp on his thumb. Kathy pulls her disgusted face, which tugs down her brow and plumps out her lips. The last six months - since her operation - Paul's seen this face too often. It's the one side of her he doesn't love.

Jake rubs his eyes: nap time. Kathy hoists him from the floor and balances him on her outslung hip. Jake reaches for his father. But before Paul can take him, Kathy carts Jake upstairs. Paul hears her footsteps overhead, the pause as she puts Jake in his cot, then the boy's cries as she leaves him. By the time Kathy reappears in the kitchen, Jake's shrieking. Paul knows that face: red verging on purple, righteous indignation in the folds of his screwed-up eyes. He resists the urge to go up to him. Paul has promised Kathy not to pander to Jake's every whim.

"Where are they getting in now?" Kathy says.

"There," Paul says, "by the back door." From an invisible gap between frame and wall an ant emerges, followed by another. Paul waits until they hit the floor, then smashes them with his shoe. Then he grabs the ant powder from under the sink and he and Kathy go outside to investigate.

They hate ants. In this, they are united.

The garden is tiny - twelve feet square - and the ants are everywhere, quickstepping in their anxious way across the concrete slabs Paul laid last summer. The slabs sit on more concrete and cement packs the gaps in between. Paul thought that this would dam the insects' flow. Instead, the ants probe for weaknesses, and find them.

Today, new horrors await Paul in the garden: winged ants, three times the size of his usual foe, are forging through the air. These ants are ungainly, like prototypes. One lands on Paul's t-shirt, a second on Kathy's ear. They flick them off. Kathy scratches a psychosomatic itch.

Paul fears there's a reason, shameful but impalpable, why he and Kathy are under siege. After all, the neighbors don't suffer this.

"I'm taking Jake to my mother's," Kathy says. "It's best for everyone."

"Not for me," Paul says. "When will you be back?"

Kathy scrapes her hair into a ponytail, which she deftly circles with an elastic band she plucks from her wrist. The air is taut with heat. The sun pounds them from a high blue canopy, marred only by the vapor trails of jets. Paul should be wearing a hat: he needs protection.

"When?" Paul says.

A plane howls above them, heading into Heathrow, and he fails to catch what Kathy says. Though he believes the word is, "Soon."

She does not look at him.

Upstairs, the baby screams so hard, his voice cracks.

"They're going under the step," Kathy says.

Paul drops to his hands and knees and finds a multi-lane highway of ants below the door. Kathy joins him.

"I can't see the entrance," Paul says.

"There," Kathy says. "There."

An ant scoots over her fingers; three weave through the hairs on Paul's. He aims the ant powder into the nest and squeezes.

Nothing happens.

He grips the bottle and squeezes again.

Still nothing.

"Give it to me," Kathy says. She snatches the bottle from him, and as she does the nozzle unblocks and ant powder explodes into their faces. It settles in their hair and in the sweat on their brows.

"Well isn't that absolutely..." Kathy says. Then she laughs. So does Paul. They dump powder on the ants, then laugh some more. Paul appreciates the moment and he can tell that Kathy does too. Upstairs, Jake drifts into sleep: his intermittent sobs are aftershocks of his earlier rage.

Then Kathy says, "Is this stuff poisonous?"

Paul reads the label: Do NOT breathe the dust.

"But what if we did?" she says. "What should we do?"

"We'll be fine," Paul says.

"Will you stop saying that? Please? I'm sick of hearing it."

"It's what I believe," Paul says. He must believe it, to make it true.

***

Kathy lies on the sofa. Even with the curtains drawn, she shades her eyes with her forearm. With one hand Paul clutches Jake to his side. With the other, he holds a chamomile tea. He places the mug on the table.

"Did you get much rest?" he says.

Kathy lifts her arm a fraction. "A little," she concedes. "Can't I have coffee?"

"If you could, I'd fetch you one."

"But I'm so tired."

"Your hands are shaking. All this caffeine is making you ill." This clinches it: Kathy's arm drops over her eyes. "And don't worry about the ant powder," Paul says. "We hardly breathed any."

"I know. That's the last thing on my mind."

This might not be true: since her operation, Kathy's become a brooder. Often Paul finds her locked behind a blank stare. That stare reproaches him. That stare says there must be more than this. Paul's trying to do his part. He'll find a job soon. In fact, he's expecting a call on Monday - tomorrow.

Paul lugs Jake to the kitchen. The boy squirms until Paul lowers him onto the cold terracotta tiles, which he gleefully slaps with a fat hand. Jake is nearly a year old. He is asserting his independence and Paul barely keeps up with him. Kathy is not the only one who's tired.

Paul searches the fridge for something to feed his son. On the bottom shelf he discovers yesterday's leftovers - half a jar of organic baby food. He dollops the contents into a bowl and microwaves it. They need a new microwave. They also need a new fridge, but not as much as they need to pay the mortgage and the interest on their car loan and credit cards. That's why Kathy's working overtime, while Paul cares for their son.

The microwave pings. Paul looks at Jake and Jake looks at him. An ant scurries past Jake's foot; another pauses on the tile beside him. Paul smashes both. Then he scoops Jake up, suppresses his wriggling and straps him into his high chair.

Paul loads a spoon with pasta and pork and tests the temperature with his tongue: perfect. Then he says, "Open wide," and he swoops the spoon down in the way Jake enjoys, with an "eeeeow" noise, like a plane coming into Heathrow.

Jake giggles and opens wide.

"He never laughs for me," Kathy says. "He never even smiles."

Paul looks up to find her standing in the doorway. "So spend some time with him," he says. "Feed him."

"I can't," Kathy says. "I'm exhausted. Anyway, what's the point? I'll never find enough time if things stay this way."

"They won't," Paul says. "We'll be fine."

"Christ," Kathy says. Paul watches her turn and walk away.

"Don't listen to her," he says to Jake. "We will be fine." He doesn't believe that Kathy will take Jake to her mother's. Her mother is a bad-tempered, self-centered woman, and - for once - that suits Paul.

***

Before Jake's bath, Paul takes him to check the flowers in the front garden. The calendulas are holding up in the heat but the sunflowers' leaves are drooping: they need attention. Across the street the early-evening sun strikes translucent flecks in the air, flecks Paul thinks are dandelion seeds buoyed by the slight breeze. Though as he squints along the street he realizes the flecks are flying ants, hundreds of them, converging on him. He sees others on the pavement, and still more emerging from the grit the ants pile up as they burrow between the flagstones.

Paul scratches his head, then hurries Jake indoors.

***

Jake stirs and mumbles; though it is ten p.m., he has just fallen asleep. He used to sleep soundly but recently he's been fitful, waking three or four times a night. Paul checked on him a minute ago. He straightened Jake's sweat-damp fringe, then took a risk and touched his upturned nose, just to feel that perfect squashy button of flesh. It struck Paul that by loving Jake so much he was putting him in danger, that loving him was an act of pure selfishness.

Paul backed away from the room.

Kathy stretches in the bath and Paul kneels next to it, on a mat still damp from Jake's bath time. Insects hurl themselves at the windowpanes. Others mill around on the ceiling, as if gathering for action. At least they're not ants.

Kathy's eyes are closed. Under the halogen spotlights, her skin is pale as French butter, punctuated with dashes of color: her nipples, the shadows in her collar bone, her slightly-parted mouth.

"What are you thinking?" Paul says.

"I'm wondering," she says, "how I can be so tired and still be alive." She raises her knee to scratch it, then lets her leg sink into the water. Her pubic hair wafts, like seaweed in a tide.

"I know what you mean," Paul says.

"Do you?"

"Sure."

"I wonder, sometimes. I really do."

With his index finger, Paul traces the scar on her left breast, the mark now faded from its original, roseate glory. Kathy opens her eyes. For three weeks after Paul discovered the lump, she thought she might die. He could not persuade her otherwise. But the lump was benign, and Kathy's surgeon excised it and sent her home with a neat line, to show that part of her was gone. Still, the effects of those weeks remain.

Paul runs his finger along the scar. Then he tickles Kathy, right between the ribs. She laughs and catches his hand. Then she squeezes his palm against her breast, pressing it flat to the bones beneath.

"Comfort me," she says.

"I'll try," Paul says. "I'll do my best."

***

Paul wakes at eight o'clock, the house silent around him. He sits up in bed. Kathy will be at work by now and although she is an expert at leaving without disturbing them, Jake rarely sleeps so long. Paul's instinct is to rush to Jake's room to rouse him. He needs to know Jake's not choking on a bead or stricken by meningitis. But there's no need: Kathy will have bobbed her head round Jake's door, before she departed. Paul lies back and tries to enjoy the unexpected peace. He thinks about last night. He smiles. But the silence nags him.

Why hasn't Jake woken up?

Paul tells himself that everything will be fine. All he must do to make it true is believe it. So he jumps out of bed, flings open Jake's door, sings "Morning, sunshine," in the direction of his cot, and then sweeps back the curtains.

When the light hits him, Jake sneezes. Then he blinks and raises his arms. Paul hauls Jake from his cot and cuddles him. Together, they are ready to face the day.

***

At nine-thirty, Jake and Paul are in the garden. Paul senses the air's tightening, presaging another day of heat. Corpse-littered ant powder lies in drifts round the door. He smiles again.

Inside, the telephone rings.

"That'll be a nice man offering Daddy a job," Paul says.

Though when he reaches the phone, the number displayed is Kathy's. She often calls around this time, if she's forgotten to leave Paul instructions - shopping, dry cleaning, Jake's doctor's appointment. Paul knows these things, but allows her to tell him.

He answers the phone. "We missed you this morning," he says.

"Oh," a woman says. "Is Kathy there?"

"Isn't she in the office?" Paul says. He thinks. "Maybe she's stuck in traffic." Though this cannot be right: even in rush-hour, it's a twenty-minute drive.

"I'll try her mobile," the woman says.

"Good idea." And as soon as the woman hangs up, Paul speed-dials that number. Kathy's phone clicks through to voicemail. "Hi," he says. "Call me when you get this." Then he says, "Last night was great. Call me."

On a hunch, Paul checks upstairs. He's in charge of laundry, so he knows every item in her wardrobe. Nothing is missing. All Kathy's make-up is on her dressing table, all her toiletries in the bathroom. That reassures him. He carries Jake to the kitchen and they drink juice while Paul considers his next move. Then he phones Kathy's mother.

"Why would she be here?" her mother says, and Paul detects a crumbling edge of worry in her voice. She is not harboring her daughter.

"What was I thinking?" Paul says. "She's gone to a friend's. Sorry to bother you."

Before he replaces the phone in its cradle, he tries Kathy's mobile again: voicemail. Where is she? He'll give her five minutes to call, then he'll find her address book and start phoning everyone in it.

Jake sits on the terracotta tiles. Paul looks at him and he looks at Paul. Jake has Kathy's mouth and ears but his eyes are facsimiles of Paul's. Paul wishes something would fill the hush, but today the planes fly a different path. He locates Kathy's address book. He picks up the phone. And as he grasps it, the phone rings. The number is the one Paul hoped for.

"Hi," he says. "Where are you?"

Kathy does not respond.

"What's this about?" Paul says. "What's the matter with you?" Then his stomach fills with cold dread. "Is there someone else?"

Kathy begins to cry. Then she says, "Would that make it easier?"

"No," Paul says.

"I'm sorry. I'm so sorry. Don't make Jake hate me. I'll call you again."

"When? When Kathy? Answer me."

"Soon," Kathy says. And she hangs up.

Paul puts down the phone. Jake watches him. Then the boy glances away and Paul turns to see what distracted him: a flying ant. Half-a-dozen more flitter round the window, seeking entry. Paul reaches for the ant powder.

"Don't worry," he says to Jake. "We'll be fine." All he must do, to make it true, is believe it.