In a monster throwdown, I’ll always rep Count Dracula over Frankenstein’s creature. But that’s not to say I don’t give Mary Shelley props for her creation; she turned a horror story into a philosophical inquiry into the nature of existence, the monkey’s paw of scientific discovery and the consequences of playing God. Her monster may not have fangs, but he’s more frightful for the ways he mirrors the dark nature of humanity.

In Sibyl Kempson’s “The Securely Conferred, Vouchsafed Keepsakes of Maery S.,” an experimental, four-part radio play presented by the 7 Daughters of Eve Thtr & Perf. Co., the woman often called the mother of horror and science fiction is resurrected and transmuted in a rambling epic that is conceptually unique but too often wearyingly opaque.

“Maery S.,” which was commissioned by Abrons Arts Center and the Chocolate Factory Theater, begins with a scholarly presentation: a rummaging through Shelley’s keepsakes — yes, “securely conferred” and “vouchsafed” — and a discussion of various definitions of “gothic” in literature, architecture, music.

Then, via diary entries, we hear from Shelley (Dee Dorcas Beasnael, who also voices Shelley’s half sister Fanny and stepsister Clarie) — a freewheeling young woman ready to embark on a vagrant life of camping, travel and reprehensible gallivanting with a young married poet named Percy.

That part is true, but “Maery S.” unravels its own fictions, strung through with anachronisms and modern language. Faster than you can say “Frankenstein,” the play transports Shelley to other places and times, including America between the 1970s and 2000s, where she road-trips in a pickup truck with the monster she dreamed up in her 1818 novel.

That’s not all: Her Bill-and-Ted-esque excellent adventure is interspersed with accounts of sightings of Bigfoot and Sasquatch, voiced by Victor Morales and Crystal Wei with the fearful solemnity of a campfire story.

“I’m juggling a lot right now, OK? Everything’s mixed up,” Shelley concedes at one point. Well said.

Kempson, who wrote and directed, is no stranger to wildly postmodern, genre-defying work, and here her Shelley is prismatic, existing, as she says, in the “space between known and unknown.”

So she recalls how Natasha Richardson played her in a 1986 psychological thriller, and speaks as a historical figure, a contemporary scholar and a sexually liberated witch-goddess (Hecate, Iris, Medusa and others are named).

Kempson’s feminist politics are provocative, as is the way the play’s structure enacts a central theme of “Frankenstein” itself. Dr. Frankenstein created the monster, Shelley created Frankenstein, and Kempson re-creates Shelley out of a mishmash of details, some real, but many fictional.

Traveling with the monster (a world-weary Brian Mendes), this Shelley proclaims how she “makes and unmakes” the world. Such moments of feminist self-actualization are riveting; for me they recall the slippery identities of the women in the work of Adrienne Kennedy and the bold declarations of the female characters in Jaclyn Backhaus’s “Wives.”

But all of the juggling is tiring; nearly four hours long, “Maery S.” gets to feel like a chore (Beasnael’s self-conscious voice performance is no help). Kempson’s idiosyncratic shifts in setting and tone (and even accents; the male Romantic writers get especially dandified affects) help keep things lively, but only when they don’t function as belabored diversions.

Case in point: the songs by Graham Reynolds, which range from sleepy folk-rock to campy pop, go on for too long. However, Chris Giarmo’s sound design, especially in the first two parts, beautifully complements the gothic themes: a feverish cascade of notes on a piano, and the feral groaning and blubbering of an unnatural creature among the chirping crickets on a dark night.

Shelley wrote a monster of a novel, and Kempson has followed with a monster of a play, large and lumbering. It’s an ambitious act, but in the electric moment of a project coming to life, something sputters and flounders, perhaps even coming apart at the seams. Just ask Dr. Frankenstein — and the woman who birthed him.

The Securely Conferred, Vouchsafed Keepsakes of Maery S.
Through May 15; abronsartscenter.org.