It’s too bad that “Madea Goes to Jail”—Tyler Perry’s latest film adaptation of one of his countless plays—is not principally concerned with Madea, nor with her going to jail. After playing the quick-witted, ill-tempered, church-resistant elderly woman in two other films (“Diary of a Mad Black Woman,” “Madea’s Family Reunion”), Tyler Perry has here subordinated the storyline of his most interesting alter-ego to a far less compelling central plot.

Like Perry’s other Madea movies, “Madea Goes to Jail” has two sets of characters: a regular cast that consists of her extended family—a recognizable bunch from the director’s other work—and a novel cast of young and attractive characters whose lives are facing hardship. In this latter plotline, Joshua (Derek Luke, “Friday Night Lights”), an assistant district attorney, sees his life disrupted when Candy, a childhood friend (Keshia Knight Pulliam from “The Cosby Show”), is charged with prostitution.

But unlike former Madea movies, “Madea Goes to Jail” fails to skillfully weave these two threads together. The movie opens with one of the few true links between the two plots: several Atlanta district attorneys meeting to review the case of Mabel Simmons—better known as Madea—who has just been charged with assaulting three cops. The lawyers will share scenes with Madea only twice thereafter; otherwise, their stories are completely unrelated, resulting in two distinct works of inconsistent quality.

The inferiority of the primary plot is due more to its execution than the narrative it attempts to tell. The tension between the two parts of Joshua’s life—his childhood in the slums and his later success as a lawyer—could set the stage for a movie on its own, as could his deteriorating relationship with his much-wealthier fiancé Linda (Ion Overman), who is also an assistant district attorney. By contrast, the storyline of Madea’s life and family offers little more than anecdotes of her problems with anger management, which she never admits to herself or to others.

What makes the two parts so disparate in quality, then, is not the stories they tell, but the ability of the actors to convey them. In a church-going family that tries to educate her, the six foot five Madea is a person of extremes: demanding yet forgiving, playful yet violent. But whether pulling a gun on her relatives at a houseparty or conveying deep hurt when her pothead brother (also played by Perry) ridicules her weight, Madea is a credible character—a madwoman played to a tee. Though it is difficult to identify with Madea, Perry knows her in and out; this is what makes her convincing.

The assistant district attorneys, whose potentially-gripping stories dominate most of the movie, are just not as persuasive as Madea and her family. Ion Overman struggles through most of the movie with one-note demonstrations of anger and shock at her fiancé’s commitment to his childhood friend, whom she solely addresses as “that prostitute.” While Derek Luke outdoes himself in a powerful scene in which he recalls the trauma that led to his falling out with Candy, his performance in the remainder of the movie lacks nuance and credibility.

The two plotlines and sets of characters continue to exist in separate dimensions until the last 30 minutes of the movie, when Madea finally goes to jail and actually interacts with a character from the central plot. But these prison scenes do not make up for the confusion caused by the unexplained back-and-forth that characterizes most of the movie.

It is interesting, however, to see what Perry makes of Madea in jail. Although the movie culminates in Perry’s traditional Christian salvation for his honest, hard-working characters, the irreverent Madea ironically becomes the moral authority over the prisoners—the only person who lectures the inmates, except the prison’s minister. For the prisoners, Madea’s words of advice—“Everybody’s got a life and what you do with that life is up to you”—provide a doctrine equal in relevance to the religious demand to surrender the self to Jesus. Madea surrenders herself to no one; this is both her blessing and her curse.

Watching the movie is a frustrating task for Perry fans and a disappointing one for newcomers hoping to learn what all the buzz is about. While Perry’s movies are often preachy, their moral messages have always been intertwined with a good amount of irony and humor, creating a balanced tension. Unfortunately, the poor structure of “Madea Goes to Jail” turns this one movie into two separate works: a unique piece of comedy that resembles nothing else and a daytime melodrama that amounts to nothing much.

—Staff writer Roy Cohen can be reached at roycohen@fas.harvard.edu.