Beatrice "Triss" has been raised in a post-apocalyptic Chicago - many buildings remain damaged from a previous war, and the city is protected by a massive fence.
To keep the peace and control human society, every member belongs to one of 5 factions, based on positive personality traits they are expected to live by: selfishness, bravery, honestly, peacefulness, and intelligence.
Anyone not belonging to these is "factionless", and forms a social underclass.
At age 16 the young adults are expected to choose a faction - either the one they were born into, or else choose another. To aid their decision, they take an aptitude test which is supposed to better illustrate their best choice.
Beatrice's test demonstrates that she could fit into at least three factions - a rare condition called "divergence".
Regarded as a threat to the stability of this society, divergents are hunted and killed.
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I didn't expect to enjoy this film.
The idea of being able to neatly divide humanity into just five different personality attributes doesn't immediately make sense.
But, psychologists have been trying this on us for decades.
And, like the Hunger Games, it becomes clear that the story is focused on internal conflict. But unlike that film, this adaptation makes a good effort to show it.
The story is clever - the concern about making the correct choices at sixteen, and sometimes going to new places as a consequence - and clearly reminded me of the real life issue to choose the right education, the right career, and the transition from familiar school to unfamiliar college.
However, the sense of danger, and stakes, grow quickly - this is no longer just about Triss - and the film roils with tension. At the end I was practically on the edge of my seat.
There's always the danger of infusing too much teen angst and ending up with a soap opera with special effects - but Divergent steers as an action thriller with a science fiction background.
There are some predictable plot elements, but many welcome surprises. The film never feels stilted or slow, and keeps a strong pace.
If the film is a reasonable adaptation of the book, then it's obvious why Veronica Roth's debut novel is such a run-away success.
This is a good story damn well told.