A Most Unfortunate Happenstance by Esther Hatch

Will the storm that brought them together be the scandal that tears them apart?
Captain John Calder has finally secured the means and standing to propose to the woman he has dreamed of since the day they met—and a house party offers the perfect opportunity to become reacquainted with her.

But a violent storm on the road to Blackwell changes everything. The cold and damp strike John down with a sudden and violent return of the ague.
Evelyn Blackwell, traveling to her family’s estate to secure a suitor for her disgraced cousin, is caught in the same storm and forced to take refuge alone in an abandoned cottage. The door flies open to reveal a fevered stranger who promptly collapses at her feet. She keeps vigil through thunder, darkness, and delirium, certain he may not survive.

But he does survive and in the morning light, they promise to leave as strangers, hopefully never to see each other again, bound only by the secret of a shared night together.
However, days later, John arrives at Evelyn’s house party. Now they must spend weeks together while Evelyn balances arranging a match for her cousin with memories of that night—memories John does not share.

The longer they spend in each other’s company, the more Evelyn wonders if her cousin’s happiness can come only at the cost of her own—and whether the storm that brought her and John together has set her heart on a course to be broken apart.