Vindicated By a Viscount by Cheryl Bolen

As Georgiana Beresford begins to unravel a sinister plot, it may be too late to save her—and the honorable man who’s offered her marriage.
While walking down a London street, Miss Georgiana Beresford nearly has apoplexy when she catches a glimpse of a woman she thought was dead. She whips around—which results in her falling into the muddy street and injuring herself. To her mortification, an exceedingly handsome man whisks her into his arms and insists on carrying her home.
Charles, Viscount Churston, had not been able to remove his eyes from the beautiful woman he was only too happy to assist. He delivers her home and learns she’s a Beresford, the sister of an Eton friend. When he calls to check on her the next day, Charles learns that his misguided act of chivalry has ruined her name. A malicious attack upon her has appeared in that morning’s London Gazette. There’s only one honorable thing to do. He must offer her marriage. Georgiana cannot deny her attraction to the handsome Lord Churston but laments that he’s only offering for her out of his sense of honor.
Once they’re joined together in a loveless marriage, he assists his bride, who’s obsessed with learning the identity of the woman who looks exactly like a one who perished in a fire.