As Harry Potter and Twilight have proved on a massive scale, the success of the Marsden books gives the film version of Tomorrow, When The War Began a large potential audience. But it has also increased the pressure on the filmmakers.

How can they possibly meet the expectations of fans who have spent years imagining in their heads the characters, the places and the drama so vividly described on the page?

Enter Stuart Beattie, who knows plenty about adapting much-loved material for the big screen. He’s the Australian screenwriter who turned a popular Disneyland theme park ride into the blockbuster Pirates of the Caribbean movies starring Johnny Depp. He also updated the classic Glenn Ford western 3:10 to Yuma for Russell Crowe and transformed a line of boys’ toys into the GI Joe movie.

Beattie, whose original screenplays include the acclaimed Tom Cruise hitman thriller Collateral, makes his directing debut with Tomorrow.

“I was instantly attracted to this project because I was looking to make a character-based but commercial action movie set in Australia that could compete on the international stage,’’ he says. Tomorrow had ‘‘all the action, but also has the heart’’.

‘‘Ellie and her friends are all wonderful, complex, engaging characters who make the ride worth so much more than the price of admission,’’ he says.

Adapting Marsden’s much-loved book was a responsibility Beattie did not take lightly.

“It’s exciting to have such popular and beloved source material because it means that there is an audience out there that really wants to see your movie,” he says.

“I take the fan response very seriously. That people actually know the story and have thought about these characters is great. It means you are not working in a vacuum so much; you are working in a world that people already know and love.”

This explains why Tomorrow, which has its world premiere tomorrow in Sydney, is the most expensive Australian movie of 2010.

Costly location shoots, special effects, stunts and elaborate action sequences were essential not only to faithfully capture Marsden’s thrilling adventure, but also to appeal to an international audience raised on a weekly diet of big-screen popcorn spectacle.

“It’s not big-budget in terms of the sort of movie it aims to be because it flat out aims at a teenage audience and they are used to seeing Iron Man and Batman and Clash of The Titans and Lord of The Rings,” Mason says.

“They’re used to seeing a lot of big things on screen so if you want to compete you’ve got to find a way to give them that value. The budget of the film may seem large in Australian terms, but it’s a very small amount of money in international terms.”

The nine-week Tomorrow shoot began in September 2009, mainly in the Hunter and the Blue Mountains.

“There was at some point a thought of shooting it in Victoria, but Victoria was very dry and it was necessary to go quite a long way from the centres in order to get the right country look,” Mason says.

“The Hunter Valley gave us the huge advantage of being within easy driving distance to Sydney, as well as having a lot of large centres in it to provide accommodation and support and having a lot of really wonderful landscapes, but also things like great looking bridges and good rivers.”

The location that originally drew the filmmakers to the region was unassuming King Street in Raymond Terrace.

“We saw it and said, ‘That’s the street, no question,’” Mason recalls.

King Street doubles as Barker Street, Wirrawee, scene of one of the book’s most nerve-wracking sequences.

“It appeared to have stayed very much unchanged for a long period of time,’’ Mason says. ‘‘It’s a unique little spot with a strong sense of an old country town.”

Once Beattie and Mason had settled on the street, they began looking around the rest of the region for other suitable locations.

“The more we settled into the area the more we realised the look of that side of the Hunter Valley was absolutely perfect for the story,” Mason says.

“If you have a project that has a lot of different sorts of locations you’re hoping to find them all close together because obviously the less time you spend travelling the more time you spend filming.”

The cast and crew ended up based in Maitland, which was handy to locations in Raymond Terrace, Dungog and Luskintyre.

“It’s an astonishingly lush and fabulously varied area,” Mason says.

“The general image of the Hunter Valley is all about the vineyards but there’s another side that isn’t as well publicised and yet it has lovely stretches of river and eight or 10 of these wonderful old bridges.

“There’s a whole lot more there than people know.’’

While interior scenes were shot on the stages at Fox Studios in Sydney, sequences set in “Hell” – the idyllic hidden valley where Ellie and her friends retreat to plan their heroics and find unexpected romance – were filmed on Sydney’s northern beaches.

“A little park tucked away in a nice little reserve somewhere,” Mason says cryptically.

But Dungog’s showground turned out to be a perfect fit for fictional Wirrawee’s showground, where Ellie first encounters the mysterious enemy soldiers.

“We ended up taking Dungog as the central reference for the town of Wirrawee,” Mason says.

Unfortunately, on the very day the crew set aside for panoramic shots of the Dungog township a dust storm rolled in and obscured it.

“So every shot of the movie where you see the town is actually a visual effects shot because we had to get rid of the dust storm,” Mason says.

“It still is Dungog, it’s just taken from still photographs and inserted into the shot.”

Luskintyre Bridge, 20 minutes from Maitland, is the setting for the film’s explosive finale.

In his book’s concluding ‘‘author’s note’’, Marsden points out that the fictional Heron River Bridge just outside Wirrawee is based on the long wooden bridge across the Murrumbidgee River at Gundagai.

‘‘Generally, though,’’ he notes, ‘‘the settings used in this book could be found in any Australian state.’’ So it was that the cast and crew of Tomorrow, When The War Began came to Luskintyre Bridge to shoot the movie’s most explosive scene.

In keeping with the filmmakers’ determination to pile on Hollywood-sized dazzle, things don’t end well for the grand old span.

“At the peak moment of filming out in the Hunter Valley we had 515,000 blocks of lights out one night with a 200-foot (61-metre) crane holding a giant 200,000-watt light to light up the whole landscape because that’s the way Hollywood movies look,’’ Mason says.

‘‘In the end the most important thing was to try and make sure that we really made use of the big frames, that we really made it feel like a big movie.

“My hope is that if you make a bigger film, if you make something that seems to actually fill that big screen in a big cinema, and the adventure is that big, then people will start to think that Australian-made stories are worthy of that.

“We have stories every bit as good as anybody else’s stories and they should be up on that big screen. So it was important to make sure everything had that feeling of scale.”

That required ‘‘a lot of physical effects on set, a lot of pyrotechnics because it’s a war and things get blown up’’.

But while it was goodnight and kaboom for Luskintyre Bridge, heritage authorities need not fret.

“We built a miniature, but it was a giant miniature if that makes sense,” Mason says.

“The pyrotechnic extravaganza was handled beautifully. Our team was led by Dan Oliver who had just finished Beneath Hill 60 and has now moved on to Mad Max 4.

“Those guys are having a good run because it’s time to blow things up again – there hasn’t been enough blowing things up in Australian movies for quite some time!”

The film has its Newcastle premiere on August 18 and opens nationally on September 2.

Asked how the Hunter locations scrubbed up in the final cut, Mason says with a laugh: ‘‘They came up looking bloody fantastic.’’

Yes, but will diehard fans of the Marsden books recognise Barker Street, Wirrawee showground and Heron River Bridge from their imaginations?

“You don’t have to be absolutely accurate and literally true to every detail in the books, you just have to keep the spirit of it,” he says.

“As Stuart keeps saying, the books will be here forever, the books are not going away, so if you see a difference between the book and the film, don’t worry, it has not destroyed the book.

“Fifty years from now the book will still be there, still be exactly the same, but the film will probably have faded from memory.”

Unless, of course, there’s a sequel. And, with seven books in the Marsden series, Tomorrow is a ready movie franchise.

Is anyone talking sequel yet?

Mason: “You can’t avoid mentioning it but it’s simply not sensible for us to get into a concrete discussion until we see if people love this movie.”

And, if they do love it, the producer expects many fans will be eager to take a Hollywood walk of fame through Raymond Terrace, Dungog and Luskintyre.

“I’d hope that if we had anything like a serious level of success with this film you’d end up with people doing tours of the sites in the Hunter Valley in the same way that fans do for films they love like The Lord of the Rings,” Mason says.

Even just to see an old bridge in the country?

“I am hoping that if people learn from fan discussion that that’s the bridge they may be motivated to travel to see it, to see if it’s still there,” he says.

“I think people will believe there couldn’t possibly be anything left of it by the time the film was finished!”