This ranging epistolary novel follows Julia Grenville, a Welsh beauty who knows little of the world until her marriage to the older Lord Stanley.
Through Julia's letters to her sister, readers learn more of Julia's new life in London - her unfaithful husband, her miscarriage, her disillusionment with the city and its fashions.
Other letters reveal that Julia has a longtime admirer, Harry Woodley, from her former life, as well as a mysterious guardian angel: her Sylph.
This character guides Julia away from the depravities of her life in London, including her gambling problem.
The Sylph is also another sympathetic ear to Julia's increasing marital dissatisfaction and growing affinity for another man, the Baron Ton-hausen.
As Julia nearly falls prey to the overzealous admirations of one of her husband's associates, her husband is consumed by gambling debts to that same associate.
She is shocked to discover the depths of her husband's ruin and plans to flee to Wales before she too can be claimed in payment.
Her disgraced husband takes the ultimate way out, and Julia goes home to her father and sister in Wales.
Her Sylph is not far behind, however, and soon reveals himself to Julia to be more than she could have ever imagined.