'Firefly Lane' Season 2 finally reveals why Kate is mad at Tully with gut-wrenching conclusion

While much of the Katherine Heigl and Sarah Chalke Netflix series Firefly Lane is focused on this dramatic but heartwarming journey through decades of friendship, in Season 2, Part 1 we finally find out why Kate (Chalke) is mad at her best friend Tully (Heigl).

We're still jumping back-and-forth between decades, from the 1970s to the 2000s, but the show takes a stronger stance on addressing social issues, like misogyny, and overall it feels like a much more emotional narrative. It leans more into a melodramatic, soap opera style, This Is Us kind of storytelling.

The highlight of Firefly Lane continues to be the loving chemistry between Heigl and Chalke, with an equally as attractive, but often more lighthearted, dynamic between the younger versions of Tully and Kate, played by Ali Skovbye and Roan Curtis.

SPOILER ALERT: Details of Season 2, Part 1 of Firefly Lane included ahead

Much of the story is focused on the 2000s storyline in Season 2, Part 1. Kate and her ex-husband Johnny (Ben Lawson) are dealing with the aftermath of the IED explosion in Iraq, while Tully is being sued by Wilson King (Martin Donovan) for leaving her talk show.

A large part of Kate's storyline is reconnecting with Johnny, trying to give their romantic relationship another shot. That's paired with moments earlier in their lives, closer to the beginning of the relationship, when Kate was seemingly leaving Tully by the wayside. Johnny is getting all of Kate's attention, while Tully is managing her tumultuous relationship with her mother.

In the trailer, you can see the aftermath of a car crash that continues to be teased throughout Season 2, Part 1, which is the link to why this loving friendship falls apart.

One night, while Tully was watching Marah (Yael Yurman), the teen gets a message from a girl she has a crush on, who invites her to the movies. Tully wasn't supposed to let Kate and Johnny's grounded daughter go out, but her godmother lets her go.

Later that evening, after Tully's had been drinking some wine, she received a call from Marah. Marah is upset and reveals that she ended up at a frat party, her crush ditched her for a guy and Marah was confronted by a boy at the party who was all over her, touching her without consent.

Tully, getting flashbacks to her assault as a teen (which we saw in Season 1), races to her car to pick up Marah. On their way back to Tully's place, someone runs a red light and smashes into Tully's car. Tully is then arrested for drunk driving, which completely collapses her friendship with Kate.

While Kate admits in the series that she misses Tully, she just can't accept an apology from someone who put her daughter in danger.

How does the Kate and Tully argument differ from Kristin Hannah's book?

While Kate and Tully have a notable falling out in Kristin Hannah's book, this part of the series does differ from its source material.

In the book, Tully tries to mend the fractured relationship between Kate and Marah, particularly as Kate's daughter seemingly idolizes her mom's friend. Tully invites Kate and Marah to hash out their issues on-camera, but it's actually a segment on overbearing mothers, and Kate feels attacked.

In the Netflix series, Season 2, Part 1 ends with a massive health scare on Kate's part, but we'll have to wait until 2023 to see if that brings these friends back together.