The Most Wonderful Crime of the Year: A Novel - Ally Carter

Knives Out gets a holiday rom-com twist in this rivals-to-lovers romance-mystery from New York Times bestselling author Ally Carter.
The bridge is out. The phones are down. And the most famous mystery writer in the world just disappeared out of a locked room two days before Christmas.
Meet Maggie Chase and Ethan Wyatt:
She's the new Queen of the Cozy Mystery.
He's Mr. Big-time Thriller Guy.
She hates his guts.
He thinks her name is Marcie (no matter how many times she's told him otherwise.)
But when they both accept a cryptic invitation to attend a Christmas house party at the English estate of a reclusive fan, neither is expecting their host to be the most powerful author in the world: Eleanor Ashley, the Duchess of Death herself.
That night, the weather turns, and the next morning Eleanor is gone.
She vanished from a locked room, and Maggie has to wonder: Is Eleanor in danger? Or is it all some kind of test? Is Ethan the competition? Or is he the only person in that snowbound mansion she can trust?
As the snow gets deeper and the stakes get higher, every clue will bring Maggie and Ethan closer to the truth-and each other. Because, this Christmas, these two rivals are going to have to become allies (and maybe more) if they have any hope of saving Eleanor.
Assuming they don't kill each other first.