She wrote somewhere around 40 novels and would have written more if she hadn't died prematurely from Bright's Disease at the age of 39. Despite her literary success, she struggled in her personal life, separating from her alcoholic husband and ultimately excluding him from her will and the upbringing of their four children. This misfortune didn't break her but rather may have inspired the many strong female characters in her novels, both good and evil.
One Night's Mystery follows the lives and loves of three young women: Cyrilla Hendrick, the daughter of handsome, penniless, scoundrel; her best friend, Sydney Owenson, a naive heiress; and Dolly De Courcy, a spirited actress. Both Cyrilla and Sydney are engaged, although things aren't as they seem in either case. Sydney's gold-digging fiance is besotted with Dolly, while Cyrilla's is arranged through her aunt, whom Cyrilla calls "the crossest, spitefulest old woman on earth." The one night's mystery of the title refers to the disappearance of Sydney's fiance the day before her wedding, but did he run off with Dolly or was he murdered?
One Night's Mystery was first serialized in New York Weekly and the London Journal before being published in book form by G.W. Carleton in 1876, toward the end of Fleming's life. It is a prime example of the type of work Fleming wrote, romantic suspense with a few Gothic elements thrown in. Her writing style is direct, her characters simple but reasonably well fleshed out, and the complicted relationships between the characters thorny and entertaining, if a tad melodramatic.
Despite the melodrama, Fleming does insert moments of poetic descriptions that are especially effective with settings, such as this one about the grim street that houses the dull and respectable Demoiselles Chateauroy school for young ladies (where Cyrilla and Sydney met):
There were no shops, there were no people; the houses looked at you as you passed with a sad, settled, melancholy mildew upon them; the doors rarely opened, the blinds and curtains were never drawn; prim little gardens, with prim little gravel-paths, shut in these sad little houses from the street; now and then a pale, pensive face might gleam at you from some upper window, spectre-like, and vanish.