Callie Thorne gets to play with fire in ‘Rescue Me’

If Callie Thorne’s Sheila Keefe had a theme song, it would be Johnny Cash’s “Ring of Fire.”

The ode to flaming desire animates Thorne’s character, who returns for her fifth season of FX’s “Rescue Me,” the testosterone-fueled dramedy about a dedicated crew of emotionally flawed New York City firefighters. And as always, her character, the perpetually high-strung widow of a firefighter killed in the 9/11 terrorist attacks, is carrying a torch for her deceased husband’s cousin, firefighter Tommy Gavin (Denis Leary).

Although most of the action of the series surrounds Gavin and his colleagues, Thorne, 39, has proved to be a reliable touchstone of the series, often stealing scenes from Leary and other cast members. Her Italian American character is known for throwing tantrums, flaunting her sexuality and relentlessly pursuing Tommy with various schemes that inevitably backfire.

“Sheila is really my alter ego,” said the dark-haired Thorne. “She does everything I wish I could do but can’t. I don’t want to go to jail.”

Her single-mother character is no shrinking violet. She once raped an unconscious Tommy after slipping him a potion containing a knockout drug and Viagra. In another instance, she took on a lesbian lover -- in hopes of making Tommy jealous -- but wound up in an abusive relationship in which she was battered and beaten.

And then there was the time she briefly kidnapped Tommy’s newborn baby and named the infant “Elvis.” This season, her character seeks help from a drama coach-therapist who tries to free her of her obsession with Tommy.

“Sheila has been off the rails from the get-go,” added Thorne. “There’s no boundaries, so it’s a tremendous amount of fun to play.”

Peter Tolan, who co-created the drama with Leary, said that, even though “Rescue Me” is man-centric (Andrea Roth, who plays Tommy’s estranged wife, Janet, is the only other female in the core cast), Thorne is a central part of the drama’s vibe: “There’s nothing we’ve thrown at Callie that she can’t handle. Her character is our Lady Macbeth, the constant troublemaker.”

Added Leary, “I stopped being politically correct about this about six months ago. We just shot for 15 months making 22 new episodes, and at one point I turned to Peter and said, ‘Callie is the greatest actress I have ever worked with.’ She’s this great dramatic actress, and she’s also a great comedic actress.”

Although a vein of wackiness will continue to course through “Rescue Me” this season, the show will not be all fun and games for Thorne’s character. Her role will get a dramatic boost by the discovery of 9/11 footage that unearths new information about Sheila’s husband that sends her into an emotional tailspin.

“That wound gets reopened, and Sheila has to cope anew with mourning and grief,” Leary said. “There’s an entire episode named after her.”

Thorne’s distinctive girl-next-door beauty has allowed her to be somewhat of a chameleon, leading to a string of diverse roles that bear little resemblance to the hyperkinetic Sheila. She was featured in “Prison Break,” “Homicide: Life on the Street” and on HBO’s “The Wire,” in which she played Elena, the former wife of Det. James McNulty (Dominic West).

But her heart is primarily with “Rescue Me,” and playing Sheila has been particularly fulfilling.

“Sheila’s really trying to be a better person,” she said. “I feel more in her skin, feel a lot more comfortable being her.”

Still, some uneasiness does creep in at times, since much of her on-screen interactions involve intense verbal screaming matches with Leary: “He’s my scene partner but also my boss, so it can be a little daunting.”

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greg.braxton@latimes.com

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‘Rescue Me’

Where: FX

When: 10 tonight

Rating: TV-MA-LS (may be unsuitable for children under the age of 17, with advisories for coarse language and sex)