You can travel the world, you can see Kuala Lumpur and the Côte D'Azur, go everywhere, try anything; but it all comes down to one moment where you realise you're about to get engaged to a deeply lovely man who is undoubtedly going to turn you into your mother.

I'm only against turning into my mother on principle. She's a lovely woman, with a habit of phoning my mobile at inappropriate moments; say, in the middle of my snowboarding session. She likes digestive biscuits and fairy tales. She lives in Berkshire; has done all her life.

"Yes," I shout, over the noise of the burners. "Yes, I'll marry you."

Tim's glorious smile, the one that I fell in love with, spreads to his ears, and over the faces of the other couple and the driver. Is driver the right word? Steerist, then. Airman. The man with his hand on the valve that makes this hot air balloon ascend, that's who I'm looking at, with his amused, patient expression that means I've seen this all before. Maybe he doesn't even believe in love any more, with all the upping and downing he's done, and so many popped questions and champagne corks. He's probably thinking, as he bends down to flip open the lid of the coolbox, that he'd never marry a person who asked that kind of death-defyingly important question in public, with onlookers. That's what I always thought, until this moment. I'm having to revise my opinion of myself.

He produces a bottle of Bollinger and four plastic glasses. "Congratulations!" shout the other couple, and the champagne is poured.

I shout, "Thanks, wow, thanks, amazing," and I can't take in the view, the soaring, razored peaks of the Rockies, because I have to drink and smile at these total strangers with expensive ski-jackets and messy, hot-air-balloon hair. That's suddenly become more important to me, making a good show. I'm my mother already.

Happy? mouths Tim.

The driver/airman/balloonist guy pulls a cord and turns a knob, and the burners diminish. We hang, for a weightless moment, and then begin to sink.

When I was little, sitting on the number 54 bus to Reading town centre, my mother would tell me stories about far-off places, and I used to ask her if they were real. I couldn't believe that there wasn't a kernel of truth in her tales of magic carpets and pirate galleons. There was one about a boy who lived on an island, a paradise, and he couldn't whistle. All he wanted was to be able to whistle. Such a small thing, and he couldn't do it; why did he make himself so miserable? My seven-year-old self couldn't understand it. Why reach for that which is beyond you? Why refuse to see the beauty of what is right in front of you?

Tim is gripping his plastic champagne glass in his enormous green ski-gloves. He's wearing a white strip of sunblock on the bridge of his nose, and he hasn't shaved for a few days, giving him a dusting of desirable stubble, and the appearance of a wild adventurer. I've known him for nine months; he's here on secondment from an insurance company in Slough. Another nine months in this country and then he expects to return home to England. With me. He has a plan: we'll find a place halfway between Slough and Oxford, and he'll help to shoulder my debts as I finish up my thesis in Molecular Patterns. It's all been worked out.

Can't real love be unsure? Can't it be delicate, wavering, affected by strong breezes? Must true love be like the mountains, so solid against all doubts?

There's a big orange butterfly sitting on the wicker basket.

With the burners turned down, I can hear the Oooooh! sounds of the other couple.

"It's a Monarch," says the driver.

One of my mother's stories comes back to me. We're on the bus, heading back from shopping on a Saturday afternoon.

There's a big orange butterfly, the King of butterflies, she says. And some tribes believe that if you capture it and whisper a wish to it, it will hold that wish for you because it has no choice but to be silent. But if you then let it go, in gratitude it will grant your wish.

I ask her, as we pass the trading estate—Is that true?

No, Penelope, she says. It's all pretend.

Back in this new life, I reach out, very slowly, and take the butterfly in my hands. I lift it to my lips and whisper to it. I can feel it listening.

"Look!" says Tim. He's pointing to a squall on the horizon, a twisting orange cloud, moving fast, shimmering, falling over itself to reach us, and then a million Monarch butterflies are in my mouth and hair and hands, and I can hear their wings beating against the balloon, a sudden thunderstorm, deafening. They surround me, raise me up on their wings; I feel them, like a hammock, and then there's no longer a basket, a balloon, a solid fiancé. There's only the air and the butterflies, taking me away, granting a wish for which I had no hopes.

Some of my mother's stories might be true after all.

I am borne away among the butterflies. The cold wind tangles my hair and makes gooseflesh of my skin, but I soon stop noticing, lulled by a spiralling kaleidoscope of rippling wings. I am safe in the giant fluttering heart surrounding me.

The soft touch of insects on my skin is ticklish at first; in the midst of their silence, I can't help laughing. I giggle my way along the Rockies, and occasionally the billowing cloud of orange and black opens to form a window of sky, or reveal a glimpse of clean white mountaintop: Grays Peak, perhaps, or Mount Evans. I don't know. Colorado is far below me, spread out like a map with no markers. Time is marked to the beat of insect wings.

Of course, eventually, I get hungry and thirsty. The fun aspect of the adventure begins to wear off.

"I want to get down," I whisper to the butterflies, and then I amend that sentiment to, "I'd like to be put down safely. Please. If it's not too much trouble." I don't feel a change in their course, and for a minute I have scary thoughts of staying up here in their ball of movement forever until I'm a skeleton, a ghost, only a strange memory in Tim's mind. But then I'm lifted upright on their wings and I feel my hiking shoes touch something solid.

The orange cloud shrinks away from me and disperses. I'm standing on the side of a freeway, next to a turnoff for a diner, the dated neon sign barely blinking in the strong sunlight. The Rockies are only a backdrop; this road is long and straight and without incline. There's nobody in sight. It's open country out here, but not desert—the ground is lush, grassy, and there's a feeling of dampness to the warm air.

It takes a few attempts at walking before my legs start moving properly. I wobble up to the diner. It's one of those flat shiny buildings that Americans seem to like, and when I push open the door I feel I've walked into the set of a movie. There are red leather booths on my right and circular stools, the kind that spin, on my left, in front of a long counter with hot plates and a coffee machine that makes a reassuring plopping sound every now and again. The smell of bacon makes my stomach rumble. I make it to one of the booths.

While waiting for someone to serve me, I try to comb my fingers through my hair, but it's one gigantic knot, as if I've just driven at high speed in an open-top convertible. Which, I suppose, I have.

I hear a door slam, and the sloppy clip-clop of rubber-soled shoes on vinyl flooring. A woman walks in from the open doorway behind the counter that I assume leads to the kitchen. She's wearing an orange dress with a black name tag, and a white Alice band in her black hair. She clocks me, and her eyes widen. She clip-clops over, biting her lips, pulling out a small pad and pencil from her breast pocket.

"Hello," I say.

"Hey. What can I get ya?"

"Coffee and a bacon sandwich please. And I'm betting you have pie, right? Lots of pie. Do you have apple pie?"

"Sure thing, hon," she says, with good humour. She is just what every American waitress should be.

"Do you have a map or something I could borrow?"

She tilts her head as she writes on the pad. "Not much call for that around here."

"For maps?"

"It's not like you get to have a say in where you're going, so, why take the time to look it up? I'll bring your coffee right over, just sit tight, hon." She gives me a reassuring smile that has the opposite effect. Why am I getting no say? What kind of diner is this?

When I begin to actually think about it, it becomes obvious that I've gone crazy and probably jumped out of a hot air balloon in order to escape commitment and this is a moment of death dream-type thing, so I hyperventilate for a while, and hit my head on the table a few times in the hope I'll wake up and find myself still alive.

When the waitress brings over my coffee, she also brings a brown paper bag. "Breathe into that, hon." She holds it to my lips and eventually I stop trying to suck up all the air in the world all at once, and settle back against the cushioned booth seat. "Don't fight it so hard, okay? You're not crazy and you're not dead. You're flying Monarch, hon. Relax and enjoy it."

"Pardon?"

"The Butterfly Express Route? To Happiness? That's what you wished for, right?"

"Not exactly." I sip the coffee. It's delicious. "I wished for . . ." What did I wish for? And why would a butterfly take me seriously?

Looking around the diner, at the empty booths and clean shiny floor, I notice pictures spaced evenly along the walls. They are all framed photographs of butterflies. The consistency calms me, somehow.

"You wished for some kinda answer," she says. "To everything. To why you are the way you are, and where you're meant to be."

I look up at her, her wiry black hair and the orange dress. "This is the weirdest dream ever."

"Hang on in there, hon. I'll get your bacon." She pats me on the arm and clip-clops back to the kitchen.

I hear, from nowhere, the theme tune to The Muppet Show.

Wait; it's not from nowhere. It's from the inner pocket of my ski jacket. It's my mobile phone. The mobile phone that was out of battery last time I'd checked. I unzip the jacket and take it out. The display says, "MUM".

"Hello?"

"Hello Pennie, love, have I caught you at a bad moment?"

"No, it's perfect timing," I tell my mother. "Listen, I'm, I'm at this place, this diner, and it's like . . ."

"Are you having some dinner? What time is it over there? I was worried you'd be in bed."

"Why? What's the time?" It's broad daylight outside, but suddenly I'm suspicious of that, of time and place and the entire universe and my assumptions about it. "Are you okay, mum? Have you seen any butterflies?"

"Butterflies? It's October."

"Listen, don't worry about me, okay? No matter what you hear, I'm okay."

"Okay," she says, her voice peppered with suspicion.

"Some stories are true after all."

"Well," she says. There's a pause. "I would have thought you'd have worked that out by now. And some truths we all rely on have never been true at all."

I can't begin to deal with that concept. "What do you mean?"

"Pennie?"

"Yeah."

"I don't like digestive biscuits."

My bacon sandwich arrives. My waitress puts the orange-rimmed plate down on the table and winks, and the phone goes dead. "Better eat up," she says. "Restroom's out back if you need it. Your ride leaves in five."

They get me down to Mexico in no time at all. Or, at least, with no helpful sign of time passing: no sunrises, no nights, and no desire to be either awake or asleep. I drift along, stopping occasionally for steak and eggs or blueberry pancakes, and my mobile remains silent. I wonder if Tim is trying to reach me. I wonder about what my mother said about the digestive biscuits. What did she mean, that she never liked them? Then why has she always eaten two of them with a small cup of tea after dinner? Why does she put them in the shopping trolley every week? The thought that she has eaten digestives against her will for decades bothers me more than the fact that I'm being carried to a new country on a cloud of butterflies.

When we arrive at the next diner I take the phone from my pocket and stare at the screen. It's dead.

I think about Tim, too. He's always in my mind.

I know we're in Mexico because there's a sombrero obscuring the neon sign and the waitress in the orange dress has adopted a terrible fake accent.

"Eh, gringo," she says, "you want the tacos?"

"Whatever."

"They are the best in all Mehico."

"I don't doubt it." I plonk myself down in the booth, and she drops the accent.

"What's up?"

"I don't know where we're going. I don't know what I'm doing. It's been one hell of a ride, but, seriously, Mexico? What's in Mexico?"

"The spawning grounds," she says, as if that were painfully obvious. "The Butterfly Biosphere reserve, on the border of Michoacán. Every October the butterflies travel, millions of them, to that one place. And there, everything becomes still. They sit on the trees. Peace reigns. It's a moment of inner contentment that few are blessed with. Trust me, things will become clear to you there. Things that weren't clear before. Like whether you should get married and why your mother never liked digestive biscuits."

"Oh," I say. "Right. In that case, I'll have the tacos."

She nods, puts away her notepad, and clip-clops back to the kitchen.

Given that such an amazing life experience awaits me at The Biosphere, I feel surprisingly calm. I think all emotion is leaving me; I'm emptying out my fear, my pain, my excitement and my happiness. Even my feelings for Tim no longer seem real. They've been chased away by the flapping of a million orange wings.

When the tacos arrive I can't appreciate their spiciness. My tongue is as dead as my heart.

It's midnight at The Biosphere. The moon is enormous, full to bursting. The butterflies cling to the black trees, spent, breathless. I lie in the grass, surrounded by the pillars of their exhaustion, a testament to their journey. Thousands of miles have been travelled.

I take my mobile from my pocket. It's dead. 

"Mum," I whisper. "I'm ready." And the phone comes to life, and dials home. My mother answers. I picture her, standing in the hall, next to the phone's cradle even though I bought her a cordless last Christmas. She's never got used to the idea that she's free to move around.

"Digestive biscuits," I say. It's the first thing that I think of.

"Pardon?"

"You don't like them."

"No, not much." She sighs. "Are you sure you're ready for this story, love? Only you've never seemed very ready to hear anything real I had to say before. Particularly about your dad."

"Yes," I say. "Maybe that's true. But I feel ready now. I'm in a different place."

"Yes," she agrees. "You sound different." The butterflies move their trembling wings to my heartbeats. "Your young man's been calling here. Leaving messages for you. He sounds worried."

"Would you ring him back for me, mum?  Let him know I'm okay? Tell him . . . I'll be in touch as soon as I can."

"Will you?"

"I don't know," I say. "I don't know yet. Tell me your story. Tell me about you and Dad."

"I moved to Napoli. Three years before you were born. Your dad was homesick, and I said I would try living there. We moved in with his mother. You're very like her. She wasn't good at listening either. That's not always a bad thing, I mean, you know your own mind. I've never been so sure as you. About anything. But I knew I didn't like Napoli."

"Why not?"

"There was nothing for me to hold on to, nothing familiar to anchor me. I felt so . . . up in the air."

"But that can be a good thing!" I say. "You've never been open to it. But to be free, to be weightless, it can be . . ."

"Can I tell you the rest?" my mother says. "Please? Right. Your dad knew I was unhappy. He tried so hard to help me settle in. The only English food he could find in the market were packets of digestive biscuits; he brought them home from work with him every day, and I didn't have the heart to tell him I'd never really liked them. His mother called them disgusting. She couldn't see what was wrong with the amaretti she made; she took it as a rejection. Which it was. I did reject her, and everything Italian. I didn't really try very hard. I can admit that now. I cried and cried. Eventually I persuaded your dad to give up his job and return to England with me. He was never really right, after that. He thought he'd let his mother down, somehow, and I didn't care enough about that to realise it would be the end of us. Just after you were born his mother had a stroke. He went back to Napoli to care for her, and after she died he never came back. I never asked him to come back, I suppose. Yes. I never once asked him to come back, and if you don't chase what you want, it doesn't happen."

"Why didn't you ask him?" I say.

There is a silence. Then she says, "So I keep buying the digestive biscuits because they remind me of him. And because I think I don't deserve to eat amaretti. His mother made the most wonderful amaretti."

"So there was one thing about Napoli you liked."

"Yes, love, I suppose there was."

I say goodbye and put away my phone. I think about what she has told me, and why I would never have understood it before this moment. But I have been weightless, babied, on the wings of a dream. I know that it is not enough to be carried away to a new place. You have to know what to do when you get there.

I close my eyes and whistle a nameless tune. I think about the place to which Tim wants to take me. I can picture it clearly. There will not be butterflies, or hot air balloons. But there will be digestive biscuits. My mother is right; I'm not like her. I know my own mind, and I happen to quite like digestive biscuits.

When the butterflies are ready to return to Canada, maybe they will touch down along the way and bring me back to Tim. I'm going to give him a real answer.