The first clarification to be made about Mitzi Peirone’s “Saint Clare” is that it has nothing to do with Chiara Offreduccio — that is to say, Saint Claire of Assisi, the patron saint of, among much else, televised imagery. Instead, Ms. Peirone’s film concerns itself more with Joan of Arc: specifically, the movie about her trial, Carl Theodor Dreyer’s “The Passion of Joan of Arc” (1928). 

It’s a great movie, the Dreyer, and a poster for it is a prominent part of the setting for “Saint Clare.” Additionally, a mantra that is stated throughout the film by its title character, Clare Bleecker (Bella Thorne), has been attributed, more in spirit than in actuality, to Joan of Arc: “Everything I have said and done has been in the hands of God. I was born to do this. I am not afraid.” That our heroine is a serial killer situated, roughly, on the side of the angels is a trope a lot of us will recognize from a Showtime series, “Dexter.”

But, then, there’s a lot of “Saint Clare” that rings a bell, some of which peals more precisely than not. Is it possible to dub something a pastiche without being able to name specific ingredients? 

Ms. Peirone’s movie poaches from a number of genres that a Boomer might recognize without necessarily being conversant with them — cheapjack horror films of a certain vintage, say, or coming-of-age comedies aimed at ’tweens. Does it come as a surprise to learn that Ms. Thorne is an alum of the Disney Channel? She was in something called “Shake It Up,” a dance-oriented sitcom in which she co-starred with the now-ubiquitous Zendaya. 

Ms. Peirone, working along with Guinevere Turner, wrote the script by adapting a novel by Don Roff, “Clare at Sixteen.” The screenplay veers from the glib to the gory, slipping, sometimes wildly, from being a straight thriller to some kind of parody. We live in an age of pop culture abundance in which some entertainments busy themselves with abstruse cultural references and easy elisions of tone. This patchwork approach, particularly when it underscores changes in taste, can be bewildering and often off-putting.

“Saint Clare” should, then, be an annoyance, a picture that draws an exclusionary line between generations. You know what, though? It’s kind of a hoot. As screenwriters, Ms. Peirone and Ms. Turner are no strangers to second-hand provocations, but what they’ve come up with is a contiguous whole marked by witty byways and a generosity of spirit. As a director, Ms. Peirone is especially fluid, possessing a sensibility in which stylistic galumphery is less its own reward than a means of expanding narrative possibilities.

Our heroine is a college-age woman haunted by a ghost — that is to say, Mailman Bob (Frank Whaley), a wise-cracking apparition who serves both as our heroine’s conscience and a clarion against future events. Past events show us how young Clare inadvertently came to adopt murder as a means of quelling various bad actors. She’s recently moved in with her pot-smoking, hippie-dippy grandmother, Gigi (Rebecca De Mornay), and is having a difficult time adapting to the new environs. A fellow student, Juliana (Juliana Le Blanc), reaches out as a potential friend, but is irked by Clare’s unreliability. Murder does tend to run afoul of one’s social schedule.

The plot? Well, it bumps along, throwing in the requisite MacGuffins and being rife with good cops, bad cops, and worse cops all in the salutary cause of divining why it is that a raft of young women have gone missing from Small Town, U.S.A. Notwithstanding some predictable curves, “Saint Clare” is grounded by Ms. Peirone’s assurance, seasoned by cinematographer Luka Bezili’s chromatic daring, and enlivened by Ms. Thorne, who proves herself a consummate movie star. She’s smart, beautiful and navigates the proceedings with rare dexterity. She’s a talent, our Ms. Thorne, and worth watching out for.