If the success of summer blockbusters is a matter of seducing your chosen audience, then The Sum Of All Fears may be the riskiest flirtation of the 2002 silly season.

Consider the competition: Spider-Man is the nimble new comic-book sensation; Attack Of The Clones is the future-past blast for hardcore Star Wars fans, millions of them.

But The Sum Of All Fears, which is the fourth in best-selling author Tom Clancy's Jack Ryan action-adventure series, is not only geared to a more adult audience, but it asks these mature fans of Jack Ryan to dramatically shift gears.

That's because the Ryan Express has been derailed and remodelled.

Fears tells the story of a looming world crisis: Euro-trash neo-Nazis plot to push the U.S. and Russia into a nuclear war that will cause chaos and destruction, but benefit the fascists in a new world order.

The hero in the crisis, of course, will be -- and has to be -- Jack Ryan. But the character is no longer a cynical, seasoned veteran saving the world with grim determination. And he is no longer played by either Alec Baldwin or Harrison Ford.

Instead, Ryan is a callow youth just starting his career as a fumbling yet clever analyst at the U.S. Central Intelligence Agency. And he is played by a callow youth, Ben Affleck, an actor who is still more reactive than proactive.

The catch is that The Sum Of All Fears is set in the present day and is not a flashback to the origins of the character. Instead, the story that was told in the 1991 Clancy book has been adapted around a younger character and relaunched.

What that means is that you simply have to forget everything you ever knew, or thought you did, about Jack Ryan and the other movies. It is not easily done and the new movie suffers an occasional credibility crisis because of it.

Nor is Affleck dynamic. Again, because of the revised character and his inexperience, the role itself is reduced in scale. Affleck himself seems small on screen, especially for a tall man. He is exploring new corners of his persona and it is not clear yet whether there is enough substance there.

That said, The Sum Of All Fears does have a lot going for it, not least of which is an absolutely horrifying plot twist. Many people already know what it is: Some spoiler journalists have given it away; the cast and crew have already spilled the beans in interviews; and the clumsy trailer has given away too much. I am not going to add to that.

Kudos, however, to director Phil Alden Robinson (Field Of Dreams) for his ability to stage the mind-blowing special effects involved in the plot twist. This climactic section of the film will devastate you. It cannot fail to do so.

Also impressive is the strong presence of Morgan Freeman as a presidential aide; the conflicted, complex performance of James Cromwell as president; and the intriguing tease of Liev Schreiber as reluctant field agent John Clark.

The Sum Of All Fears is not, however, a fast-paced thriller. Instead, it is a lumbering giant that asks a lot, and perhaps too much, of its audience before it delivers the goods. (More on Sum Of All Fears)

(This film is rated AA)

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