Is it possible to make a liberal vigilante movie? In The Brave One, Jodie Foster plays Erica Bain, a mousy Manhattan talk radio host who’s closer to Ira Glass than Rush Limbaugh. When she wants to discuss American violence, she quotes D.H. Lawrence and Emily Dickinson, not Clint Eastwood’s “Make my day” speech. And when a caller suggests that the vigilante who’s been gunning down street thugs is doing the city a service, she cuts him off, looking mortified at such right-wing blather.

Which is odd, since Erica herself is the vigilante. But this latest from Irish director Neil Jordan is an odd movie. Where one might expect a rabble-rousing female version of Death Wish, it’s actually a study in grief and ambivalence, as moody and murky as the director’s Oscar-winning The Crying Game. Also like The Crying Game, it pivots on the unlikely but compelling relationship that develops between two unhappy people — here, Foster and an insomniac homicide detective played by Terrence Howard (Hustle & Flow). Like the lovely London hairdresser in that other movie, Foster’s character has a secret, though the “equipment” she’s concealing is a 9-millimeter automatic. Will Howard, who’s investigating the vigilante slayings, find out? And will he care?

It all starts when mild-mannered Erica takes the dog for a walk in Central Park with her hunky doctor fiancé (Naveen Andrews of “Lost,” just as under-used here). When muggers jump the couple in a tunnel and begin beating them, Jordan fractures the violence in a way that distances us, showing us much of the action through the viewfinder of the attackers’ video camera. (Yes, these thugs belong to the YouTube generation.) Erica wakes from a coma to find her lover dead and her life empty, except for a nagging fear that something like this might happen again. She buys a gun, and when the occasion arises, she uses it — first in what might still be construed as self-defense, then in increasingly tepid blood. When trouble doesn’t find her, she starts to look for it.

Vigilante dramas have their roots in Elizabethan revenge tragedies, which carried the pious message that “an eye for an eye” merely perpetuates the cycle of violence. At the same time, they catered to the audience’s desire to see bad guys bite it. For all its subtlety, The Brave One does the same thing. The city Erica experiences is a paranoid’s fever dream, with evil lurking around every corner, and Jordan and the screenwriters put us in a position where it’s hard not to cheer for her when she pulls a Bernhard Goetz. But we also see how her own violence sickens and bewilders her, even as she starts to depend on the rush she gets from being judge, jury and executioner. Foster’s taut, slow-burn performance makes all this plausible — though it should be noted that she does more husky, anguished whispering than Haley Joel Osment in The Sixth Sense.

The screenplay hints that Erica’s story might be a parable for something bigger, like the situation of New York — or America, for that matter — reeling in the wake of a horrific surprise attack. “I always thought that fear belonged to other people . . . until it touched me,” Erica tells her listeners. References to the war and suicide bombers suggest that the movie is an elegy for more than just one woman’s innocence.

But hackneyed TV-cop-drama devices pull The Brave One down, as does an ending that’s too muddled to resolve anything. Howard does amazing work as the detective, who seems to be half courting this perp and half waiting to pounce on her. Too bad, when he finally decides what to do, the movie gets cheesy. Erica’s taken way more than an eye for an eye at that point, and we’re left wondering exactly who’s going to save the city from this liberal gone postal — or her from herself.