★★

The last Divergent movie's box-office score of nearly $US289 million worldwide has failed to dispel the impression that the series is The Hunger Games' poor cousin.

The two franchises have much in common. They're both drawn from best-selling novels for young adults and both feature super-athletic female heroes battling for survival in dystopian future worlds run by smooth-talking despots with a special mandate to make life miserable for the young.

But there the similarities end. Unlike Jennifer Lawrence's action woman, Katniss Everdeen, who's mastered the art of looking as if she knows what she's doing, Divergent's Tris Prior (Shailene Woodley) seems chronically bewildered. It's as if she's forever trying to catch up with her body as it performs one CGI-assisted feat after another.

And she has reason for her puzzlement. Allegiant is the third film in the series and the plot is now hopelessly convoluted and desperately in need of a laugh. Some cross-fertilisation would have done it. I kept wishing that those clowns from The Hunger Games – Elizabeth Banks' Effie Trinket and Stanley Tucci's Caesar Flickerman – could have been flown in to administer light relief.

When the film opens, Naomi Watts' Evelyn has just taken over as ruler of Chicago, which has long been a walled city in the midst of a wasteland devastated by chemical contamination. The megalomaniacal Jeanine (Kate Winslet), the city's former ruler, is dead and things should be fine except that Evelyn, too, is starting to play the despot.

Tris and her lover, Four (Theo James), who happens to be Evelyn's son, decide it's time they explored life beyond the walls. They escape, braving a trek through toxic dust, together with an acid rain downpour, before finding themselves in another cocooned city run by yet another Hollywood name. It's Jeff Daniels and he's cast as David, the suspiciously suave director of a high-tech empire with the ominous title, Bureau of Genetic Welfare.

There are all sorts of big themes buried amid the confusion: collective comfort versus individual freedom, the hazards of human engineering and the persecution of deprived minorities by the rich majority. But the story is so thoroughly upstaged by CGI gadgetry that you hardly have time to sort out the cast list.

It's not so much a plot as a revolving door where recurring characters can be glimpsed from time, behaving much as they have always behaved.As with The Hunger Games, box-office returns are being maximised by dividing the last book in the series into two films.

So there's one more to come. It can only improve on this one, which manages to seem cluttered and empty at the same time.