I've been out all day, the sky is the colour of a ripening bruise and I'm shattered. All I want is to put on the answerphone and make some lemon balm tea and watch Wizadora with my kids pressed against me on the sofa.

My partner puts his head around the door. "OK," he says. "We've got to deal with The Creature."

"What, right now?"

"It's getting worse," he says. "It's either dying or going crazy. We've got to get it out - fast."

"There's no one we can call in?"

"Of course there bloody well isn't."

"I don't want to do it."

"Do you think I do? Come on, it's down to us."

For two days now there has been a mystery animal scratching behind the cast-iron Victorian fireplace in his second-floor study. If it got in, it can got out. We've been waiting and hoping.

Yesterday, he phoned the RSPCA. "Sorry, I don't know if you can help me - do you deal with squirrels? Well, we think one might have fallen down our chimney - at least, something has been squeaking and scratching for more than 24 hours now ... no, I don't think it's a bird, it's sort of heavy ... do rats fall down chimneys?"

The RSPCA said they really needed the public to handle this kind of thing themselves. They advised opening up the chimney and quickly throwing a blanket over whatever emerged.

"Could it bite me?" my partner asked brightly, in the voice he uses for negotiating an overdraft. Well, they said, squirrels do bite - but only when cornered or attacked.

OK, so you've been trapped in the dark for 48 hours and then you drop into a room with two large animals standing over you with a blanket. Do you feel at all cornered?

We give the children strict instructions not to move from the sofa (I see this vicious, feral thing tearing around the house looking for young thighs to savage) and we go up to the study, where Amstrad and papers have been covered with a dust sheet.

"I just don't think we should do this alone," I say again. I'm not being scared, I'm being sensible. Anything could be up there. We're not vets or farmers, we're puny city dwellers. Just cleaning out the stick insects causes trauma.

We freeze at the sound of claws scraping across brick.

"Julie," he says. "Pull yourself together. Take a deep breath and count to 10."

We arm ourselves: two vacuum cleaners for the ash and brick dust which will come out as soon as we open the sealed fireplace. Two blankets for chucking over. A large wire cat cage (open, lid poised to drop). A cricket bat ("I'm quite prepared to kill the fucker," says my partner). And the metal salad tongs - to yank it down if it gets stuck. We pull on stout gardening gloves. I look longingly at his old fencing mask, hanging on the wall, but don't say it.

With all appliances switched on, my partner begins pushing at the metal plate which covers the aperture. I stand, matador-like, with my blanket.

The suspense is unbearable. I feel like that nervy blonde in The Birds. There is something alive in there which we cannot see and which in seconds will be before us. It will almost certainly be ravenous and distressed. It will want to bite.

As my partner shoves the cast-iron plate backwards, the hole widens and an avalanche of brick dust and soot begins to fall. We flinch back, waiting for the body. "Could it be rabid?" I whisper, fear knocking the breath back in my throat.

"That does not even merit an answer," he hisses. Just then, the phone rings - on the desk, under the dustsheet.

"Oh Christ." We kill the vacuum cleaners. It's his script editor. "Can I call you back?" he says. "An animal is at this very moment about to fall out of our chimney. Can you give me five minutes? Sorry."

"Jonathan!" I freeze. A grey bushy tail just licked into view for an instant. I move forward with the blanket. "A squirrel!" (I had secretly feared a rat.)

We hold our breath. More and more dust falls, occasionally larger pieces of brick and concrete. Panicky, clawed scuffling. For three seconds a head hangs in the gap - grey nose, black eyes, quivering. Slender grey paws holding the chimney arch - then gone again.

"Shit!" Jonathan grabs the salad tongs. I hold the cat cage open.

The head bobs down again and we don't have to do anything because it loses its footing and it's in the basket. We slam down the lid. We're both trembling. Now we have it in captivity, we realise it's only a baby - big head, quivering, lost.

We carry the basket to the far end of our lawn. The children trail out for a look. Once free, the poor thing still won't run. It's disorientated, starved, probably blinded by the light. It lopes around our feet, giddily, eerily tame. It tries to climb on Chloe's tricycle.

"Who's been feeding Prozac to this squirrel?" our neighbour and her son ask five minutes later as it ambles on to their terrain. We explain. We're worried it's easy meat for cats or foxes now.

But her son just picks it up gently, cradling it in cupped hands, carries it to the relative safety of a tree. I think of all our weaponry upstairs. It's been a draining half hour.

"Kids!" says my partner dismissively, swiping a dandelion with the cricket bat. We go inside to feed spaghetti to our own menagerie.