Stay with Me by Jody Hedlund

Sacrificing and dying to oneself is costly.
But doing so brings new purpose and joy.

As a private investigator, Sybil Huxham has seen her fair share of strange occurrences. But nothing in her career has been more perplexing than the miracles she’s witnessed as a result of people drinking ancient holy water. When she discovers more of the rare holy water, she experiences strange overlaps with a nobleman in the Middle Ages who is languishing in a dungeon, accused of treason and condemned to die. To save his life, she finally crosses to the past completely.
Nicholas Worth has never met a woman quite like Sybil, and as the two run for their lives into the Weald, they find refuge among a community of outlaws. With both their reputations on the line, they have little choice but to marry. As they get to know each other, an undeniable attraction develops. But danger and disease chase after them, drawing ever closer. Will they be able to escape the threats? And will Sybil choose to stay with Nicholas in the past, or will she be ripped apart from him forever?