Lila (Viola Davis), left, loses a son in a drive-by shooting but finds a vengeful new friend in Eve (Jennifer Lopez), whose young daughter was killed. (Bob Mahoney/Samuel Goldwyn Films)

Viola Davis can do tragedy, earning Academy Award nominations for such heartbreaking roles as a Jim Crow-era maid in “The Help” and the mother of a troubled student in “Doubt.” In “Lila & Eve,” the actress has plenty of opportunity to demonstrate those skills as the grieving single mother of Stephon (Aml Ameen), a teenager killed in a drive-by shooting.

But when the movie suddenly switches gears into a revenge fantasy, she’s on less solid footing.

Davis plays Lila as a woman coping with loss any way she can — pills, wine — and struggling to be present for her surviving son (Ron Caldwell). More constructively, she’s in a support group called Mothers of Young Angels. It’s there that she meets Eve (Jennifer Lopez), a grieving mother whose anger makes her stand out in a crowd of meek figures so brittle they seem like they could break at any moment. After Eve’s young daughter was killed, the police didn’t bother investigating, she tells Lila, warning her that the same thing might happen with Stephon’s as-yet unsolved murder.

Eve has a point. The two detectives assigned to the case (Andre Royo and Shea Whigham) haven’t made much headway, and they don’t even bother returning Lila’s calls.

At Eve’s instigation, Lila decides to do some of her own detective work. In a convenience store parking lot, the women confront a drug dealer who they suspect may be connected to Stephon’s killing. Before you know it, that young man is also dead, and the pair are fleeing the scene. This paves the way for a string of “Death Wish”-style vigilante justice and a rapidly rising body count.

Davis is an excellent actress, and her poignant scenes of woe aren’t the only standouts. Ameen and Caldwell have a natural rapport in their scenes together, and these lighthearted flashbacks, in which Lila is seen joking around with her two boys, are effectively bittersweet.

At moments such as these, this Lifetime Films production asks viewers to take “Lila & Eve” seriously. Although Lopez — the reigning queen of cinematic camp with this year’s “Boy Next Door” — is in the movie, the story nevertheless raises important questions about the way police assign task forces to investigate the deaths of white cheerleaders but not those of young black men.

And yet the movie, directed by Charles Stone III, is content to point to such thought-provoking notions without fully examining them, letting the bullets fly instead. Every time Lila seems like she might apply some morals to her quest, the movie pulls back. When a mother of two murdered brothers comes to the support group, Lila hardly reacts, despite the fact that she’s the one who killed those boys.

It’s at this point that the plot holes start appearing, in advance of a twist ending that’s hinted at so aggressively it’s nearly impossible not to see it coming. By the time the movie reaches its finale, with a “Home Alone”-style booby trap, any trace of seriousness has been blown to bits.

In the end, Davis ends up a wasted resource. She does her best to elevate the material, but the story fails to live up to her considerable talents.

R. At Angelika Pop-Up at Union Market. Contains strong language and violence. 94 minutes.