My Gentleman Spy by Sasha Cottman

Former spy William Saunders’ world is turned upside down the day he rescues missionary worker Hattie Wright from the deep blue waters off the coast of Gibraltar.

When circumstances compel them to share a cramped cabin on the boat trip back to London, desire and passion ignite between them. Hattie sees the time with Will as a brief respite before she goes back to her mission among the poor and vulnerable in the slums of London.
Will, however, feels honor bound to offer her marriage and return her to the world of privilege she once knew. Despite her heart’s desire to possess his love, Hattie is determined to continue her important work. She rejects his proposal.

But Hattie has made powerful enemies in the criminal gangs of the rookeries and there are those who would gladly see her dead. When Hattie goes missing, Will is finally forced to face the truth of his past to save the woman he loves.