What Did Tully Do to Kate on Firefly Lane ? Season 2 Finally Reveals the Answer

COURTESY OF NETFLIX

Firefly Lane season 2 is finally answering the show's biggest question: what did Tully do to Kate?

Based on the book of the same name by Kristin Hannah, the first season of the Netflix series follows two women named Kate (Sarah Chalke) and Tully (Katherine Heigl) throughout their decades-long friendship.

As the series recounts various years of their life, it jumps back and forth through time, leaving viewers to connect the pieces as the story progresses. While there are plenty of shocking moments throughout, the first season really leaves viewers guessing as a flashforward to Kate's father's funeral reveals that Tully and Kate are no longer on speaking terms … or even friends.

While there have been numerous theories about why the longtime friends are fighting during the show's hiatus, season 2 finally gives an answer. And Heigl was right: "It's pretty big."

Read ahead for everything to know about the big season 2 revelation and how it strays from the book.

Warning: major spoilers for Firefly Lane season 2 ahead!  

RELATED: 'Firefly Lane' to End After Supersized 16-Episode Second Season

What did Tully do to Kate on the show?

After taking time apart, Kate and Johnny finally decide to give their relationship another shot. As they celebrate getting back together in their home, Tully agrees to watch their daughter Marah, who was recently grounded.

While at Tully's apartment, Marah receives a text from a girl named Ashley, whom she has been crushing on, asking her to go to the movies to see The Notebook. Despite Kate and Johnny giving Tully strict instructions that Marah isn't allowed to go out, she decides to let her go anyways after seeing how excited she is.

As Marah goes off with her friend, Tully runs into her former boyfriend Danny, whom she learns actually lives in her building. The two eventually share a pizza together in her apartment, where Danny later reveals that he has a girlfriend. After he leaves, Tully pours herself a few glasses of wine before getting a distressing call from Marah.

Marah reveals that after the movie, she and Ashley met some guys outside the theater, who invited them to a frat party. When they got there, Ashley started texting her ex-boyfriend to make him jealous, and he ended up showing up at the party and leaving with her. She also reveals that she met a guy who gave her beer and was all over her so she went to hide in the pantry.

Getting flashbacks of her own sexual assault when she was younger, Tully rushes out the door to come to Marah's rescue. She safely gets Marah out of the frat house and the two drive home together. However, as their light turns green, someone runs a red light and smashes into their car, badly injuring Marah.

Though Tully isn't at fault for the accident, she is arrested for driving under the influence. Not only does the incident badly damage her career and make her lose a big job deal, but it completely destroys her friendship with Kate, who refuses to speak to her.

After leaving her numerous voicemail messages, Tully is relieved when Kate finally texts her agreeing to meet at her house. However, once Tully arrives, she quickly learns it was Marah who texted her, hoping the two friends can make amends. Kate is furious but agrees to talk to Tully, who uncharacteristically takes full responsibility for her actions and apologizes. Though Kate admits that she has missed Tully as well, she tells her that she doesn't accept her apology and they're no longer friends.

What did Tully do to Kate in the book?

Like on the show, Tully and Kate's rift does revolve around Marah but in a completely different way. In the book, Tully is still on The Girlfriend Hour with Johnny as her producer. As the two work together, Kate's old jealousies about Tully rise up, especially after Marah starts to idolize Tully.

With Kate and Marah's own relationship falling apart, Tully asks them both to appear on the show to work out their issues. However, it turns out that the show's segment is actually about overbearing mothers, which Kate is furious about. Kate storms off the show and Johnny decides to quit the show as a result. As a result, Kate and Tully completely lose contact with each other, despite still missing each other as friends.

"One of the things I think that's been fun is that we have kept some big moments from the book and been very true to those, and then there are other things that we've done that are different," showrunner Maggie Friedman previously told to Entertainment Weekly about the show and book differences.

"I hope that people who are big fans of the book, can watch the show and be like, 'Oh, my God, there's that moment I remember!' And also be like, 'Oh, I'm surprised by this, but it's cool because it's in the spirit of the book, but it's a different thing.'"