It's odd to see Kristen Stewart with her girlish face and petite figure in full U.S. Army combat gear, an assault rifle at her side.

The Twilight star seems entirely too small and fragile for her role as Private First Class Amy Cole in writer-director Peter Sattler's feature debut Camp X-Ray.

But that's precisely the point: Stewart, 24, and her young costars are about the same age as most of America's serving men and woman. They look like high school and college classmates.

An uneven and, at times, even disappointing indie drama, Camp X-Ray is about the complex relationship between a military guard and a detainee at Camp X-Ray, the infamous detention facility at Guantanamo Bay or "Gitmo."

Stewart's character is a gung-ho soldier, eager to please her superior officers and prove her mettle. Newly assigned to guard duty, she learns through the course of the film a few ugly truths about the cost of war and about herself.

Her first lesson: Never use the word prisoner to refer to those behind bars at Gitmo. That would acknowledge they are actual prisoners of war and that they come under the protection of the Geneva Convention.

International laws, rules of war, and codes of chivalry don't exist in Gitmo.

But Sattler isn't interested in mounting a polemic or making a political stand. His story is more elemental and intimate, centering on the strange friendship Amy develops with one of the prisoners Ali Ami (Peyman Moaadi, A Separation).

She meets Ali while making the rounds with library books. He complains bitterly that the prison doesn't stock the final Harry Potter book. Calling her "Blondie," he says he is desperate to find out if Snape is a good guy or a villain.

A hostile Amy assumes The Prisoner of Azkaban is an Arabic text.

At one point, Ali throws his feces at her.

Eventually, Amy begins transgressing against iron-clad rules laid down by her sexist, racist bullying supervisor, Corporal Ransdell (Lane Garrison, Prison Break): Do not engage with the detainees, and never disclose personal information.

Stewart and Moaadi have great chemistry, delivering believable, moving performances.

Camp X-Ray raises quite a few fascinating questions about power, sexism, and war, yet fails to explore them in any real depth. More troubling still, it's a character study that does little in the way of character development.

Camp X-Ray **1/2 (out of four stars)

Directed by Peter Sattler. With Kristen Stewart, Lane Garrison, Peyman Moaadi, Tara Holt, John Carroll Lynch. Distributed by IFC Films.

Running time: 1 hour, 57 mins.

Parent's guide: R (profanity, implied violence, brief nudity).

Playing at: PFS Theater at the Roxy.