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It’s hardly the cheery advertising fare that billboards typically shill: “Raped While Dying/And Still No Arrests/How Come, Chief Willoughby?” But with black letters on a red background, that’s what the titular signage reads in Three Billboards Outside Ebbing, Missouri, writer-director Martin McDonagh’s drama that’s as deadly serious as his 2008 film, In Bruges, yet just as funny.

The billboards are the brainchild of Mildred (Frances McDormand), the mother of the slain girl who wants to call attention to the case seven months after the crime occurred. She believes that Willoughby (Woody Harrelson) and his hapless crew haven’t done anything to try to catch her daughter’s killer; when a local TV news team interviews Mildred about the billboards, she claims that the police department “is too busy torturing black folks” to bother with crime.

This is a shot at Officer Dixon (Sam Rockwell), who allegedly beat a black man in custody. Though the subject is obviously topical, McDonagh quickly drops it, using the detail to paint Dixon as a subpar cop rather than make a statement about racism among our country’s law enforcement. It’s therefore a bit of a distraction, and far less effective than the director’s more unremitting and entertaining approach of portraying Dixon as a clown, with jokes ranging from him being not too bright to living with his mama.

But this is Mildred’s story, and she’s a force. She tears into the priest who visits her home to tell her that the town is against the billboards (she insinuates that he’s a pedophile) and objects when the dentist brings up the matter (she turns his drill on him). Mildred doesn’t soften even when Willoughby, after telling her the details of the investigation, confides that he has cancer. But McDonagh is careful not to let her be an unrelenting hardass: She has guttural moments of grief as well as moments of goodness, from righting a bug that’s stuck on its back to getting Willoughby help when he suddenly coughs blood on her. Mildred’s anger is born of despair, not a desire to be wicked.

The film expertly gives the main characters their moments without detracting from the main story, and does so with dialogue that’s Hell or High Water-style offbeat and witty. McDormand’s performance is formidable: Her Mildred is at once steely in her resolve to see justice and amused at the bumpkins around her, a state that the actress precisely projects with subtle changes in her expressions. But Rockwell comes very close to stealing the show, with Dixon being both the butt of the jokes and the source of them. Very few of his scenes are in earnest, and Rockwell is a convincing lunkhead.

Though there are two arsons, a suicide, and a man thrown out a window during the course of the film, its through line is keeping the billboards in place despite the resistance Mildred faces. There’s a chilling scene in which she comes face to face with her daughter’s potential murderer, and by the film’s end, she and an unlikely partner figure out a way to seek a more general revenge. But even then, they’re not sure. Three Billboards ultimately demonstrates what it’s like when you’re out for blood but not soulless enough to get it.

Three Billboards Outside Ebbing, Missouri opens Friday at Landmark E Street Cinema and Bethesda Row Cinema.