Writer-director Karen Moncrieff made a fairly auspicious debut in 2002 with “Blue Car,” one of the better coming-of-age pictures of recent years. Her new film, a multi-part film surrounding the discovery of a serial killer’s most recent victim, is considerably more ambitious, but while it serves as a showcase for some terrific performances, it achieves the wrenching drama it’s aiming for only intermittently.

“The Dead Girl” begins with an episode titled “The Stranger,” in which a wan, bedraggled young woman (Toni Collette), continually browbeaten by her bedridden mother (Piper Laurie), discovers the body of a young woman while walking in the field beside their isolated home. Finally having had enough of her mother’s insults, she abandons the house and goes off with a supermarket clerk (Giovanni Ribisi) who’s interested in the corpse—and in her. This portion of the film is gritty and atmospheric, but the performances, especially by Laurie, who outdoes her operatic maternal turn in “Carrie,” are rather over-the-top.

Next up is “The Sister,” starring Rose Byrne as a forensics grad student who believes that one of the corpses she’s assigned to work on is that of her long-absent sister, even though her mother (Mary Steenburgen) and father (Bruce Davison) resist the idea. The pall that her sister’s disappearance has cast over the family’s life is so great that even the romantic interest of a fellow student (James Franco) can’t rouse the girl from her depression.

The middle segment, “The Wife,” is unquestionably the best, a virtual one-woman tour de force for Mary Beth Hurt as Ruth, a slatternly woman who complains bitterly when her drab husband (Nick Searcy) goes off on another of his long drives. During his absence, she has to take over his job at the storage facility next door, and when renting out a unit she discovers what appear to be the trophies taken from victims of the serial killer. How she deals with the information makes this the film’s most genuinely unsettling episode, with texture and punch.

Almost as good is “The Mother,” in which Marcia Gay Harden gives an exceptionally affecting performance as the mother of the girl whose body was the subject of the first two episodes. In her grief she goes to her daughter’s last residence, a run-down motel, where she meets the desperate hooker (Kerry Washington) who was her roommate and best friend and discovers why her child left home and how far she’d fallen. Unlike the thoroughly bleak story that preceded it, this segment’s close has a degree of hope to it.

But that doesn’t last long, because the final episode shows us the final hours in the life of the dead girl, Krista (Brittany Murphy), a hot-tempered prostitute who fights with her brutish pimp (Josh Brolin) and then hitches a dangerous ride trying to reach her daughter on the child’s birthday. This is the least impressive of the picture’s five sections—theatrical, overwrought and obvious—and it closes the film on a down note in more ways than one.

Moncrieff has written some effective scenes here, and she’s drawn some strong performances, especially from Hurt, Harden and Collette. But though the smaller roles have been starrily cast, most of the other performers are just adequate, and in a few cases (Laurie, Murphy) less than that, and the narratives don’t manage to maintain a dependably sharp level, though Michael Grady’s subdued cinematography, with its washed-out colors, and Adam Gorgoni’s moody score are distinct pluses.

There’s a good deal to admire in “The Dead Girl,” but like so many anthology pictures with largely independent stories, it lacks consistency in both content and execution. It’s sporadically powerful but too often tedious and self-important.