As railway station reunions go, it's pretty short on passion. It takes a few moments for her to pick him out of the bustling crowd on the platform and when their eyes lock in the instant of recognition, his smile curdles. About half a dozen emotions flicker across his face in the few seconds it takes him to stride the dozen metres that separate them. Then he takes her in his arms and whispers in her ear, "I'm home."

The scene plays out near the end of Home By Christmas, the new movie by prolific Wellington filmmaker Gaylene Preston, which previews on Anzac weekend before opening on April 29. A seamless and assured blend of archive, dramatisation and reconstructed interviews, it tells, mainly in his own words, the war story of Preston's dad, Ed, who enlisted in 1940 on the way home from footy practice in Greymouth and pacified his pregnant wife, Tui, with the assurance that "we'll probably be home by Christmas".

The fact that it would be Christmas 1944 before he embraced her on that platform is one of many bracing ironies in this film, whose power and resonance belies its modest scale. Among the others is that it's a film about memory, whose major character is very careful about what he remembers and what he chooses to forget.

It's not Ed and Tui embracing on that platform of course, but actors. Hollywood-based Shortland Street veteran Martin Henderson plays the wartime Ed and, in a nicely symmetrical piece of casting, Preston's daughter, Chelsie Preston Crayford, plays the young Tui. "By the time I was ready to film, she was just right for the role," says Preston. "So I thought: 'I'll get her now before she gets too expensive'."

What we know - and Ed doesn't - as they embrace, is that during his long absence a romance has developed between Tui and another man.

We've heard the story before, in Preston's 1995 film War Stories, in which seven women, among them Tui Preston, recalled their experiences at home. Tui told an interviewer then that a dalliance "did develop into a sexual thing".

"I'd never enjoyed sex but I did enjoy it with him," she said. "He taught me to have confidence in myself. He wanted me not to go back to Ed but that was not going to happen. I had a son and if I had left Ed, they would have taken my child off me."

Ed, who died three years before War Stories was made, never saw Tui's electrifying confession. But Preston says it wouldn't have told him anything he didn't know. Hence the platform scene, rich in haunting ambivalence, dense with unspoken thoughts.

"I think," she says, in a tone that makes it plain that she knows, "he took one look at her when he got off the train and thought: 'Something's gone down and as long as I don't let her talk about it, it'll be fine'."

That's the guts of it, really: Home By Christmas is a film full of talking, but it's also a film remarkable for what is not said. The "interviews" are actually re-enacted - the older Ed is played, with pitch-perfect control, by Australian actor Tony Barry, the mad Mini driver from Goodbye Pork Pie and the present-day Preston, only a few years his junior, interviews him. But it's based closely on audio interviews Preston conducted with her father years before. Ed was dying of cancer and finally agreed to his daughter's oft-repeated requests to share his memories. "But he knew there was a lot of stuff he wasn't going to tell me."

As the film makes clear, Ed Preston's was a short war. Captured by the Italians after three weeks, he spent much of his time in a POW camp and, when Italy surrendered, he escaped to Switzerland.

"My father's secret about the war is that they all went off to have a party and he actually did," says Preston, laughing. "He spent a year living in the Churchill Hotel on the shores of Lake Geneva and he couldn't get out. But his lips were completely sealed on the subject of what happened. Whatever he did in Switzerland went to the grave with him.

"Whenever I asked him about it, he would say 'the tucker wasn't very good'. What a way to sum up a year of your life. And whenever he gets to a bit where there might have been a bit of how's your father, he starts describing in detail a meal he ate."

Ed's reticence was about more than his possible peccadillos, says Preston.

"It can be very disturbing. He can be very frank about some things but when he's talking about the battles he'll say 'so we had to take this hill, which we did' and under that 'which we did' was a terrible battle."

So Ed is not so much an unreliable narrator as a judicious one.

"He's terribly reliable. He's reliably clear about not telling me stuff that is none of my business, especially as he knew that he was going to die ahead of my mother and he didn't want to leave the cheeky girl in the family with information that could hurt Tui."

War Stories and Home By Christmas are, in their different ways, celebrations of a discretion that went out of fashion. Tui, recalling that platform meeting, admits to us that "nothing was said the next day. We never talked about anything. We sort of stumbled through it." Ed, meanwhile, "told his story in a loving way", Preston says. "I think the film reflects that huge cleverness of a simple man.
"It's a celebration of the non-therapy generation. Everything doesn't necessarily get better if you talk about it; it can actually get worse. It may - but it also may not - create catharsis."

And that generation's habit of holding its tongue hides another truth, says Preston: "Under the happy-ever-after bright light of the 50s and 60s there was a shadow. I've spent a lot of my creative life exploring the shoreline of that shadow."

Born in 1947 in Greymouth, Preston was Tui and Ed's second child. Her elder brother Ted is a senior civil servant and her younger sister Jan is a Sydney-based boogie piano legend (who, not incidentally, composed the music for Home By Christmas). Ed ran the local fish and chip shop and the family home - the only books in the house apart from the Bible were about the royal family - scarcely sounds like the crucible of great artists. But Preston still says her destiny was set by her upbringing and education.

"They lived in a participatory culture," she explains. "Ed's sister played the piano for silent movies and Ed could do a fantastic Buster Keaton act. I remember when I first saw a Buster Keaton I thought 'Buster's doing Ed's tricks'.

"And we were also the lucky generation, who got cooked to middle class by the great Clarence Beeby educational experiment of play-based and art-based education."

So there was a wide artistic streak in the young woman who headed to Britain in 1969 on the endless OE that was common at the time. And her filmmaking career was born in, of all places, a psychiatric hospital near Cambridge. She took a job as the assistant librarian, whose duties traditionally included organising the Christmas pantomime.

"We had these patients doing drama therapy. We were happy with the improvisations they were doing but they weren't. They wanted an audience, they needed someone to clap. This I can understand.
"If we were going to turn what they were doing into a play, we would be kind of institutionalising the drama therapy, keeping it in the same place all the time. So as a practical solution, we decided to film it on 8mm and cut out the bad bits."

Preston was working with another staff member who suddenly eloped and she had to learn how to edit the footage (on the kitchen table) and project the finished product.

"The sound was on this huge old BBC tape recorder and the projector was so little that if you pressed the button too hard it would wobble. But if you pressed the two buttons more or less at the same time you could have this film. And those people, who were pretty well ignored all the time, suddenly became visible.

"And I thought it's good fun to do and I'd rather have a film of what we were doing in drama therapy at this time than sit down and write an erudite report that will be read by three people."

The film that resulted was called The Animals and the Lawnmower - "alas, a seminal lost work", says Preston, feigning extravagant grief - and it sparked the passion that has seen her compile a filmo-graphy, as director or producer, of a dozen documentaries and half a dozen features.

Deborah Shepard, who interviewed five women, Preston among them, for the 2009 book Her Life's Work, identified the two strands that distinguished her work as "a feminist sensibility and a desire to give people a voice on film".

The description is apt when you consider her subjects, from women who've had mastectomies (Titless Wonders, 2001) to the pioneer trade unionist Sonja Davies (Bread and Roses, 1994). She's also produced other women's films about airline "trolley dollies" (Coffee, Tea or Me, 2002, directed by Brita McVeigh) and a New Zealander murdered in East Timor (Punitive Damage, 1999, Annie Goldson).

"It's not mainstream-movie fodder," says Preston. "Those women who sat on the railway line [in Bread and Roses] are not featuring hugely in the way it was."

So there's Preston, back from England in 1976, lured by the promise of a then-renascent film industry. "I thought I could just go home for a year or two and give it a burl and see how I go," she says, "and I'm still here."

It was a remorselessly blokey filmmaking culture she encountered, she remembers, and when she adds that "I get treated very well" you get the sense both that the good treatment was hard-won and that a few poor souls who didn't treat her well may have been given reason to regret that at the time.

"It could be that the landscape has changed. It could be that it changed only very briefly. I always gauge things from watching the news and looking at how many women versus men speak with authority and how many women versus men are victims over a day a week a month. I think it's kind of reverting, that people think 'we've done all that [feminism] and now we can stop worrying'."

Conscious that she owes her parents' generation a huge debt of gratitude for the life she has, Preston is also conscious of what is owed to her generation.

"We fought, too," she says of the campaigning feminist cohort she was a prominent member of. "We fought for this generation to have the freedom that they've got. We fought for a time when you could not fight for it but just have it. But unfortunately we also live in an amnesiac age and in an attention-deficit age. You can't expect a generation who doesn't know what they could lose to be rigorously defending it."

I cannot forbear to ask Preston how she deals with critics. We haven't spoken since I gave her last feature, 2003's Perfect Strangers, a pretty hostile review and got some hostile fire in return, mainly from a couple of add-water-and-shake columnists. My words hang in the air for a moment before Preston replies that it's "a bit of a loaded question".

She's anxious to assure me that "all the stuff that went down after your review wasn't run by me" and I haven't the faintest idea what she's talking about. It transpires that Helen Clark - who is not, Preston says, a personal friend - was furious about the review and didn't mind who knew.

"People thought I must have put her up to it but I had nothing to do with it," Preston says. "But it went on and on and on. She was still mentioning it three years later. She'd open a building and mention your review."

Plainly, I'm going to the openings of the wrong buildings, because it's all news to me. But if Preston is - or ever was - personally hurt by the review, she's not letting on now.

"I know people who can recite their bad reviews. I can't. I put them into two piles. 'Got It' and 'Didn't Get It'."

In preparation for this interview, I re-watched the film, a self-described "chilling romance" about a one-night stand that turns into a cross between ghost story and gothic farce. I'm not about to change piles.

"If they got it, great," Preston continues. "My job is a persuader. I persuade the story into a script and I persuade the script on to the screen by persuading actors and cinematographers and editors and other creative people to make a film that persuades audiences. And if it doesn't persuade a key reviewer, it can be bad luck but it can also be a matter of persuasion."

"What does that mean?" I wonder.

"It means you have to look at what the work is and ... Look, you're going to get bad reviews. I've had a bit of a charmed life. I knew Perfect Strangers was a film that would polarise audiences. I think I made it on purpose to do that."

Like any local filmmaker and all but a few artists, Preston isn't going to get rich.

"In financial terms I'm not rich. But the life I live, my foremothers couldn't imagine. What I do has made me rich in so many other ways I can't quantify it. I suppose telling our stories is making a contribution, especially in a country where our stories are not usually told. Storytellers mine the culture, and that's wealth that is both unquantifiable and priceless. And I'm very, very pissed off with Taika Waititi."

"What for?"

"Because he's so bloody cool. I'm sitting here, I'm waiting for the phone to ring. Where's my Hollywood offer? I could be an action hero's friend. [Waititi has just been cast in a film about comic-book superhero Green Lantern].

"Oh, well," she sighs at last. "He can't help it, I suppose. That's a cross he has to bear."

So while Waititi fights to save the universe, Preston will keep walking what she calls "the dusty roads" of telling our stories rather than "driving the freeway" in Hollywood.

"The home crowd is the hard crowd and I'm a filmmaker who's chosen to concentrate on the home crowd. Why? Because I grew up without any New Zealand stories in the public space. They were all over the private space but not in the public space. So my creative life has been about putting those private stories into the public space and if people don't understand it at the time, over time they might."

*Home By Christmas previews Anzac weekend and opens at cinemas on April 29.