Belmary House Book One by Cassidy Cayman

Tilly Jacobs thinks spending a month in London helping her history buff cousin catalog antiques in a possibly haunted mansion that’s slated to be torn down will be the perfect thing to help her get over being fired from her job. Possibly proving the existence of ghosts will just be icing on the cake.
When her ghost turns out to be a living, breathing, Regency era earl who mistakenly drags her into his century, she thinks she’s in for the best vacation of her life. All she has to do is enjoy the scenery, which includes the hunky Lord Ashford, until he can get her back to her own time.
She doesn’t count on getting caught up in finding his missing sister, or on a murderer being after them, or the fact that if the house gets destroyed, so do her chances of ever getting home. Least of all, she doesn’t count on the undeniable attraction she feels to the mysterious and brooding Lord Ashford, or the fact that his life involves things far more difficult to believe than she ever thought imaginable.