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Katherine Heigl stars as Tully, left, and Sarah Chalke as Kate in "Firefly Lane," a new Netflix series.

On the quiet streets of Firefly Lane, two girls formed an inseparable bond, born from trauma and loneliness.

Netflix’s new series “Firefly Lane,” which premiered last week and is based on Kristin Hannah’s 2008 novel, spans three timelines: the teen years in the 1970s, college and first jobs at a television station in the 1980s and adulthood in the 2000s. The music changes, the fashion changes, the men change. Kate Mularkey and Tully Hart change, too, but across decades, they change together.

“You do see all of the pitfalls and the challenges they overcome, and their bond is stronger for that,” Sarah Chalke, who plays Kate, told the Daily News. “They’re like family. They met at 14, bonded over a tragedy and are just there for each other for the long haul.”

The timelines weave in and out, a tangled web of high school crushes and the Iraq War. Chalke and Katherine Heigl, playing Kate and Tully in the ’80s and ’00s, bounce off each other with ease, through work problems, boy problems and mom problems. Through ups and downs, promotions and divorces, Kate and Tully are always there for each other.

“It’s not always easy and it’s not always smooth. They have conflict and they fight,” showrunner Maggie Freidman told The News. “But in the end, they are platonic soulmates.”

It’s always the two of them, even when Johnny (Ben Lawson) squeezes his way into their relationship in the ’80s, personally and professionally.

“He gets sucked up into their whirlwind,” the Australian actor told The News. “For the next 20 years, he becomes part of The Kate and Tully Show.”

As their younger selves, Roan Curtis, 25, and Ali Skovbye, 18, stepped into Kate and Tully’s shoes, respectively. In fringe and oversized glasses, a friendship is formed between next door neighbors, out of a common need to love and be loved.

“They’re both in such a period of feeling lonely and needing someone to talk to and be vulnerable with,” Skovbye, who plays the younger version of Heigl’s Tully, told The News.

Due to production schedules, Curtis and Skovbye didn’t get as much time to work with their older counterparts as they would have liked, although Curtis joked that she was prepared to emulate Chalke because she had grown up watching “Scrubs.” So instead, they found ways to make teenage Kate and Tully their own, giving them time to grow up.

“As we’re growing into television...you get more dimensional teenage characters and I think that with that comes more complex real world issues because teenagers are people too,” Curtis told The News. “They have problems. They have big problems. Your teenage years, for some people, are the toughest in your life.”

The transition between decades is aided by the fashion, a hilarious mashup of white jeans and hot pink heels with matching tights. At one point, Chalke and Heigl don full ’80s aerobics outfits to go undercover for a story at the TV station, where Tully works as an on-camera reporter and Kate a producer.

“(The clothes) just made slipping into the younger version of Tully a little easier. Trying to remember what I felt like at 20, 21, I think I had more energy and I think things hurt less,” Heigl joked. “I had to walk like my back isn’t out and I gotta be excited about the day ahead like I’m not already exhausted. The clothes really helped.”

“Firefly Lane” balances the trauma with the joy. For every broken promise, there’s a karaoke dance scene. For every broken heart, a sweet bonding moment. But for every delight, there is a tragedy. But at the same time, it feels real. Friedman joked that her goal is to make you call your best friend at the end of every episode to say, “I love you.” As Tully points out in one heartbreaking episode, everything she and Kate go through is a shared experience with millions of women.

“My favorite movies are ‘Steel Magnolias’ and ‘Terms of Endearment’ and ‘Good Will Hunting,’” Heigl told The News. “Movies that are really, deeply human stories where you get to watch these flawed individuals who have a million strengths but also plenty of weaknesses. It just makes you feel less alone for a minute. That’s what I loved so much about this, too.”