HOW do you follow up your debut film when it's been a box office smash hit and garnered Oscar nominations into the bargain?

In the case of writer/director M.

Night Shyamalan, you again cast Bruce Willis in another suspense thriller, this time as David Dunn, sole survivor of a devastating train wreck.

The film is called Unbreakable, and co-stars Samuel L.

Jackson as Elijah Price, a mysterious stranger who offers a bizarre explanation as to why David escaped without a single scratch.

It is an explanation that threatens to change David's family and life forever.

M.

Night Shyamalan had not even finished editing The Sixth Sense when he started developing ideas for his next project and came up with the concept for Unbreakable.

He had been working on another story when he suddenly had an idea about a man who starts questioning his purpose in life after walking away from an horrific train crash.

"For some reason, the other movie I was working on just didn't seem like the right next step," recalls Shyamalan.

"I wanted to go forward in scope and implications for something that would really capture the imagination and this idea lends itself to that.

It was a great canvas as opposed to the other idea which felt like it was very similar to The Sixth Sense."

He wrote the script with Willis and Jackson in mind as the two main leads, despite having no idea if the two actors would agree to star.

"I couldn't believe it when Night called and said he was already working on another script and that he was writing it specifically for me," says Willis.

"We had just finished shooting The Sixth Sense, the movie had not even been released in theatres yet, and he already had a new idea and wanted me to star.

I was so impressed by his confidence in me and, having just worked with him, I knew what he was capable of, so I trusted him implicitly."

Samuel L.

Jackson also had the same kind of instinctual trust about Shyamalan and the script.

"I had read The Sixth Sense a few years ago and thought it was an awesome script," he says.

"So not only did I trust his writing, but I also had spoken to Bruce about his experience working with him and trusted his opinion about what he had done.

So I said, just let me know when it's ready and I'll be there."

When the writer presented his script to producer Sam Mercer, he was knocked out by the results.

"My initial reaction was 'Wow! He's done it again!,'" says Mercer.

"What impressed me the most was the level of detail and layering, which I thought far exceeded The Sixth Sense.

"It is clever, inventive, emotionally grinding and incredibly riveting with even stronger and richer characters.

As a piece of writing from a young writer/director, it really is two more giant steps further along."

Just 30-years-old, Shyamalan says the film represented a personal progression: "I implemented a whole different theory of filmmaking on The Sixth Sense that was just beginning, and this is kind of the evolution of that - like that was the bachelor's degree and this is the master's.

Hopefully it will be sort of a signature in that you can tell it is by the same filmmakers - very suspenseful with a lot of twists and turns and emotion - but with a whole new story and excitement."