Milkteeth by Caitlin Starling

Practical, unassuming Jane Shoringfield has done the calculations, and decided that the most secure path forward is this: a husband, in a marriage of convenience, who will allow her to remain independent and occupied with meaningful work. Her first choice, the dashing but reclusive doctor Augustine Lawrence, agrees to her proposal with only one condition: that she must never visit Lindridge Hall, his crumbling family manor outside of town.

Yet on their wedding night, an accident strands her at his door in a pitch-black rainstorm, and she finds him changed. Gone is the bold, courageous surgeon, and in his place is a terrified, paranoid man—one who cannot tell reality from nightmare, and fears Jane is an apparition, come to haunt him. By morning, Augustine is himself again, but Jane knows something is deeply wrong at Lindridge Hall, and with the man she has so hastily bound her safety to.