WARNING: Spoilers for the ending of "Firefly" After watching Netflix's "Firefly" in its entirety, you'll be (what did Tully do ......) ), you're probably grieving (what did Tally do? ......), (how could she end the series like that?), (how could she end the series like that?) ) and outraged that they ended the series the way they did (opens in a new tab). Now you are probably wondering what the ending of Kristin Hannah's book "Firefly No Hikari," on which the series is based, is all about, and if the book's ending is a clue for the series' second season (opens in a new tab). At the very least, you'll be hoping to get answers about how Tully and Kate's friendship, played by Sarah Chark and Katherine Heigl (opens in new tab), fell apart. [Because the book version of "Firefly" answers some (emphasis on some) of your questions. Fair warning: yes, it's sadder than the scenes at Tully and Kate's funeral. When you find out what happened to your favorite Firefly Lane girls, be prepared to weep.

Season 1 of the series ends with Kate telling Tally that she can never forgive her for what she did. We don't know exactly what Tally did, but if you read the book, you may find the answer.

In Hannah's book, Tally tries to get Kate and Marla to appear on "The Girlfriends Hour" to repair their relationship. However, much to Kate's dismay, the segment is actually about overprotective mothers and the damage they do to their children. In other words, Tally is on national television condemning Kate's parenting.

Furious, Kate flees the show. Johnny, Tully's producer and Kate's husband in the book as well as the series, exits the show in solidarity. Humiliated and hurt, Kate believes that her friendship with Tally is over for good.

So is that what caused the rift between the two on the show? Showrunner Maggie Friedman (opens in new tab) told Entertainment Weekly (opens in new tab): "One of the things I think is fun is that we keep some big moments from the book and are very loyal, and we do different other things we have done."

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Worth noting is that Marla and Kate seem to be getting along well at Bud's funeral (Bud, may you rest in peace). Tully quit The Girlfriends Hour at the end of season 1, before the betrayal occurred.

And it's possible we won't find out in Season 2. Heigl told Collider: (Open in new tab) "I always thought the reason for (Kate and Tully's rift) would be revealed in Season 2. But maybe not. Maybe it's something that we can really pull out."

I know, I know. In the series, the ominous funeral flash-forward led us to believe that Tally was sick and probably dead. However, it turns out that Tally is pregnant and that Kate's father, Bud, is a dead man.

In Hannah's book, it is Kate, not Tally, who begins to show horrible symptoms. Kate is diagnosed with terminal breast cancer, and Tally rushes home from a news trip to reconcile with her. They reconcile, and Kate asks Tally to take care of Johnny, who is still married (they are not divorced in the book), and Mara when she is gone. And then Kate leaves this world. I know: even darker than the series' slightly darker ending. (Rowan Curtis, who plays young Kate, told Oprah Mag (opens in new tab): (opens in new tab) "I've never cried so much reading a book. The ending of Kate's story feels so unfair.")

"Unsatisfied" Hanna's "Firefly" has a sequel (opens in new tab). In that book, Tally and Kate "reunite" when Tally is in a coma after a serious car accident.