The Whispering Night by Susan Dennard

The forest is more dangerous than ever in this highly-anticipated, pulse-pounding, and swoon-worthy conclusion to the bestselling Luminaries trilogy.

Winnie Wednesday’s future is looking bright. Hemlock Falls is no longer hunting the werewolf, she and Erica Thursday are tentative friends, and Winnie finally knows exactly where she stands with Jay Friday.
With everything finally on track, Winnie is looking forward to the Nightmare Masquerade, a week-long celebration of all things Luminary. But as Luminaries from across the world flock to the small town, uninvited guests also arrive. Winnie is confronted by a masked Diana and charged with an impossible task—one that threatens everything and everyone Winnie loves.
As Winnie fights to stop new enemies before time runs out, old mysteries won’t stop intruding. Her missing father is somehow entangled with her search for hidden witches, and as Winnie digs deeper into the long-standing war between the Luminaries and the Dianas, she discovers rifts within her own family she never could have imagined.

What does loyalty mean when family and enemies look the same?