At the Mercy of Midnight by Chloe Cullen

Amelia Winslow and Silas Finley are rival scholars who have spent years trying to outsmart one another, until a fateful discovery binds them together in a way neither is able to escape. When they are cut by a pair of ancient daggers, they become bonded against their will and transported to each other every night at midnight by a magic that seems to be unraveling before their eyes.

Desperate to break their bond, they discover darker truths and deeper bonds and wonder at whether the Midnight Blades are far more dangerous than either suspected. Hunted by a secret order and racing against the bounds of time, Amelia and Silas must work together or risk losing more than their freedom.

Because if they fail, midnight may never come again.

Book One of the MIDNIGHT REALM Duology.