Director Jonathan Mostow's biggest success so far was writing and directing the Academy Award-winning WWII submarine movie "U-571", starring Matthew McConaughey and Harvey Keitel. As well as facing the daunting task of filling James Cameron's shoes on the "Terminator" franchise, "T3" is also the first film he's directed that he hasn't written himself.

You've written the movies you've directed before. As a storyteller, why pick up somebody else's story here?

I initially thought it's definitely nuts to take it on. Who'd want to put themselves in a position to be compared to James Cameron? But I realised I was a fan of the first two movies and I thought, What would I want to see in a third movie? As I began to think of ideas for a story I became more and more invested in it.

Can you explain the dynamics of working with Arnold - he's integral to the project, yet you're the director...

I think they realised to make "Terminator" work, there has to be a filmmaker's vision behind the movie. When I started this I was not shy. I said, "Here's the movie I'm going to make, here's how I'm going to do it. If you don't want to do it my way, you should find a different director."

Did Arnold test you at the start?

Although I haven't asked him directly, I assume Arnold had director approval. I sat down with Arnold and told him the kind of movie I wanted to make and he was not only supportive, but immediately had great ideas for it. It's the ideal situation if your movie star is also interested in first and foremost telling the story.

The history of the third film in a franchise is always a bit dodgy - "Alien³", "Superman III", "Jaws 3", the third "Batman" - history isn't on your side!

Yes, the number three has not been a good one. The reason usually is the studio rushes out another one for business reasons. They rush it out for a holiday weekend. They think, Just get the script as good as you can, we have to shoot! It's hard to get a good script together, and I didn't proceed with this movie until I thought I had a script that was really working. I have Arnold Schwarzenegger, the famous character of the Terminator, a huge budget, and big special effects in this movie, but in my opinion the star of the movie must always be the story. If you don't have that, you shouldn't make the movie.