In 1996, 17-year-old Azula Nakamura is invited by her estranged mother, Ursa, to spend Christmas and New Year with her and her half-sister in Hira'a. Unsure she'll ever get an invitation like this again, Azula accepts, asking if she can invite her 'good friend' Katara to come as well.
Katara Enuaraq, still mourning her mother's death, is furious at her father for inviting his new partner to move in with their family. When her secret girlfriend tells her about the invitation, she accepts the chance to get out of the house - even if it means spending December with strangers.
So at the start of the Christmas season, Azula and Katara pack their bags and set off for the small, cosy town of Hira'a.
They vanish without a trace, and according to Ursa, they never arrived.
Over a decade later, a Polaroid photo is found tucked between the pages of a library book. It shows two teenage girls bound, gagged and utterly terrified. One is from the Fire Nation, the other from the Water Tribe.
And the book came from the Hira'a Public Library.
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An idea that's been buzzing around my brain for a while.