Canadian actress and musician Jill Hennessy stars in the new drama Lymelife. (Matt Carr/Getty Images)Actor Jill Hennessy is giving off rock-star signals. She's carrying a guitar. She also swears breezily, and often ends her sentences with "Man," a word delivered in that defining deep, serrated-edge voice.

"Should I pull a Billy Bob?" she jokes, settling in for an interview in an office at the CBC Broadcast Centre in Toronto. "Don't mention my movie! Don't talk about my acting!"

'I couldn't not do [Lymelife]. You don't see a lot of roles like that. The mother is usually just a peripheral character, and not really affecting.'

—Jill Hennessy

Hennessy is far too earthy – dare I say, Canadian? – for the kind of entitled idiocy Billy Bob Thornton recently displayed in this same building. At 18, Hennessy moved to Toronto via Edmonton and Kitchener, Ont., to study acting. To eat, she busked in the subway, as well as slung milk shakes in the Eaton Centre and survived murder mystery dinner theatre. (She recalls with glee the day a fellow waitress took a stale dinner roll and lobbed it at the head of a groping customer.)

That Hennessy, 40, is both warm (big laugher) and cool (she's owning her Stevie Nicks boots) in person is somehow not surprising. Unlike movie stars, the people who come to us through television are the ones we feel we know: miniature, unthreatening and in our living rooms.

For six years, Hennessy played a medical examiner on the hit NBC series Crossing Jordan, but she really became famous in the early '90s as DA Claire Kincaid on Law & Order. Without Billy Bob-style vituperation, she points out, "I started off as a musician. I was surprised when I got Law & Order. It was a great gig, but I had to quit my band to do it, which was kind of sad."

Hence, this particular moment is a happy union for Hennessy's two sides. Her first full-length album, Ghost in My Head, will be available online in June, and this Friday her acclaimed, melancholic film Lymelife opens in Canada.

Brenda Bartlett (Hennessy, left) and son Scott (Rory Culkin) live with family pressures in a suburb affected by Lyme disease. (Cinema Vault)The Ice Storm -y drama (with comedic patches) of familial disintegration in the '70s features Hennessy as Brenda Bartlett, a mother of two teenage sons stewing in a wealthy Long Island suburb. Her husband, played by Alec Baldwin, is an unfaithful real estate developer getting rich quick, but Brenda grieves the simpler life the family left behind in Queen's.

Hennessy, flaunting a thick New York accent, is the film's moral centre, an anxious mother of two who duct-tapes her son's clothes to his body to ward off insects bearing Lyme disease, a looming threat to the community.

Hennessy landed the part one week before shooting began, an issue only because she had an 11-week-old baby at home.

"I couldn't not do it. I recognized this character. Everyone feels like, if I were a better wife or woman, my husband would love me, my kids would love me more. She comes full circle and makes a very bold choice. You don't see a lot of roles like that. The mother is usually just a peripheral character, and not really affecting."

To help her manage making a film while parenting two boys (a newborn and a four-year-old), Hennessy had an assistant close by. But she still ran between scenes to pump breast milk in the nurse's office at a local school in New Jersey (the budget didn't allow for trailers). Available cast members held the baby, including the two Culkins, Rory and Kieran, who play Hennessy's sons, and Emma Roberts (niece of that other Roberts, as her frog smile attests).

"Alec would hold baby Gianni and always make him laugh, which drove me crazy. How does he make everyone laugh, even a three month-old baby? It kind of pissed me off," says Hennessy, smiling.

Most women with a three-month-old are still stumbling in the darkness of exhaustion and adjustment, but Hennessy prescribes moviemaking for post-partum malaise.

"I think it helped me get through that time, in retrospect," she says. "It got me outside, stopped me from focusing on the sheer lack of sleep and the daunting situation of having two kids. It forced me to delegate. I highly recommend it."

Lymelife is a slice of adolescent autobiography written by two brothers in their early 30s, director Derick Martini and Steve Martini, who also scored the film. Brutality wends beneath the pretty surfaces of these New Jersey subdivisions; at one point, Baldwin and his eldest son burst into a bloody bar fight over the patriarch's promiscuity.

Family members Scott, left, father Mickey (Alec Baldwin) and Brenda are forced to deal with Mickey's marital infidelity. (Cinema Vault)"All of it is based on reality," says Steve Martini. "It was sometimes hard to watch because you've lived through it, then you live through it again as it's being filmed. Watching the footage and editing it, you're editing your life. It's been cathartic."

While common in the real world, the subject of a family on the edge of splitting is rarely touched upon in movies, with a few notable exceptions, like The Squid and the Whale and Shoot the Moon. "I think it's too terrifying for people," says Hennessy. Her own parents separated when she was "12 or 13."

"I remember that feeling of incredible fear and incredible discomfort. Fear is the bottom-line emotion. I could relate to [my on-screen son], in a way, to his desire and fear of change. It's, 'Maybe we shouldn't change anything. Maybe if I don't say anything about it, it'll go away.' Divorce is a terrifying prospect."

Hennessy has been married for eight years, but her latest birth will be the album, which she recorded in Austin, Texas. She's a singer-songwriter with a coffee house purr – a slightly rougher Tracy Chapman – digging into the big themes of death, loss, and loneliness. Whatever the quality of the work, Hennessy is, of course, setting herself up for mockery at worst, indifference at best. It's the rare actor who crosses over to musician with credibility – the battlefield is littered with dead efforts from Michael Damian to Robert Downey Jr. to Billy Bob himself.

"This is what I love doing. Everyone is going to have their POV, but I have to say to myself, if I were on my deathbed, would I say, 'It's really good that I didn't try that film or music project because someone might not have liked it.' I don't think my last breath should be me saying, 'I'm so glad I didn't try.'"

She gestures toward her guitar, propped against the wall. "People might think it's a vanity project. But somehow singers are allowed to go act. Look at Dwight Yoakam: he's an amazing actor. You know, it's all storytelling in the end."

Lymelife opens in most Canadian cities on May 8.

Katrina Onstad is the film columnist for CBCNews.ca.