When your job is executing death row prisoners, it’s best not to have a guilty conscience. But after ending the lives of eleven men — the last in a botched procedure — the job has been getting to warden Bernadine Williams. Now, as she has to oversee the lethal injection of a twelfth doomed inmate, Anthony Woods, she’s mentally exhausted, she can’t sleep, and her marriage is falling apart.

The warden has to deal with doubts about Woods’ guilt, last-minute efforts to save him by his attorney, anti-death-penalty protestors chanting outside her window every day, and family issues involving both Woods and the parents of the victim. Williams runs things by the book, but not as harshly as previous movie prison wardens, like those played by Bob Gunton in “The Shawshank Redemption” and Patrick McGoohan in “Escape From Alcatraz.” Unlike them, as a woman in a man’s world, she can’t afford to let anyone inside the walls see her personal cracks, even as she ensures Woods is treated with respect, despite his date with death.

Alfre Woodard — who hasn’t gotten nearly enough leading roles in her career — is outstanding as Williams, so stoic on the job and so vulnerable at home, where Wendell Pierce is solid as her husband. Aldis Hodge plays Woods as a man who alternates between desperation and hope, with Richard Schiff as his lawyer pursuing every opportunity for clemency from the governor. The scenes between them — and between Woodard and Schiff — are master classes in patient acting. The rest of the supporting cast includes Vernee Watson (whose career started on “Welcome Back, Kotter” in the 1970s) and Michael O’Neill (memorable as Secret Service agent Ron Butterfield on “The West Wing”).

“Clemency” was written and directed by Chinonye Chukwu, in an impressive full-length feature debut. My only complaints are with some of the pacing in the final third and the film’s overall darkness (a problem that may be due to a not-bright-enough bulb in the projector at The Tivoli, where the movie was screened this weekend at the St. Louis International Film Festival).

I give “Clemency” — which won’t go into general release until the end of the year — an 8 out of 10.