Love in Disguise by Carol Cox
When costume-maker Ellie Moore suddenly finds herself out of a job in the middle of a bleak Chicago winter, she uses her knowledge of theatrical disguise to secure a position as an undercover operative with the Pinkerton Detective Agency. Her assignment: find the culprit behind the theft of silver shipped from the mines near Pickford, Arizona.
Disguised as Lavinia Stewart, a middle-aged widow, Ellie begins her investigation. Soon she finds she must also pose as the dazzling young Jessie Monroe, whose vivacious personality encourages people to talk.
Mine owner Steven Pierce is about to lose his business after the theft of several bullion shipments--until hope arrives in the unlikely form of Lavinia Stewart, who offers to invest in Steven's mine. In his wildest dreams, Steven never expected to be rescued by an inquisitive gray-haired widow...or to fall head over heels for Lavinia's captivating niece, Jessie.
But then the thieves come after both Lavinia and Jessie. Ellie isn't safe no matter which character she plays! Will she be forced to reveal her true identity before the criminals are caught? What will Steven do when he discovers the woman he loves doesn't exist?