His Duchess in Disguise by Emma Linfield

A mysterious maid. A secret. A terrible choice…

Groomed to be her estranged father’s ticket to social ascent, Miss Emma Hoskins lives in a cage. When her father, Lord Calber, announces that he bet and lost her hand in marriage to a heinous man, she does the first thing that comes to mind. She flees.
There are few things Leo Brady dislikes and being Duke of Menhiransten is at the very top of his list. Especially when hiring a new maid nearly lands him in the grave.
Accused of kidnapping Emma by the man hunting her, Leo is willing to do anything to protect her. Even dig up the most painful aspects of his past.
As they quickly realize, crashing a wedding is not nearly enough. The only way to unmask the greatest treason London has ever seen is by staying apart forever.