When Sophy Stanton-Lacy's father leaves for Brazil, he arranges for his daughter to stay with her aunt's large family in London. The Rivenhalls agree, thinking they'll be doing this "poor motherless girl" a favor - but when Sophy arrives, she throws them for a complete loop by being sprightly, competent, witty, and fun. She sets about cheering and improving her aunt's family and disentangling her cousins from unwanted (or unpromising) alliances: her cousin Cecilia from a poet; and her ill-tempered cousin Charles from his engagement to the thoroughly unpleasant and colorless, but eminently suitable, Eugenia Wraxton.
Chaos, hilarity, and romance quickly ensue.
While Sophy has the family's best interests at heart, she isn't above manipulation to get there. She especially goads her cousin Charles' temper and goes against his orders (in order to teach him that he is not in the position of authority he thinks he's in). In a major plot point, she is willing to do something that places her in a disgraceful light in order to bring about her desired ends. However, Sophy is also brave to a fault, very loyal, and very kind. Other virtues, such as fairness, familial love, and discretion, are exhibited or applauded by the characters.
Note, though, that the Rivenhalls are hardly a straitlaced family: periphery characters are said to have their share of vices, most of which are glossed over by their relations. One character gambles, but this is presented as foolish behavior and not condoned. Some flirtation takes place. Charles has a violent temper and often, when in a rage, says things he later regrets; but he is also kind, temperate, has a good head on his shoulders, and recognizes right when he sees it.
While not specifically a moral issue, "The Grand Sophy" does feature a Jew portrayed as a shrewd, wicked money-lender. This stereotype may be seen as antisemitic, or it may simply be a characterization based on the position of many Jews as bankers during this era.
Practically none. There is no mention of God (except when His name is taken in vain) or the Church.
A character is threatened and threatens at gunpoint. Charles is known to be an excellent boxer and there is some talk about his possibly doing bodily damage to several men. One man is shot, sustaining a slight wound. The possibility of duels is broached.
Drug and Alcohol Content
Alcoholic beverages are mentioned and consumed.
Sophy's uncle - and, indeed, her father as well - is said to be a womanizer, which does not seem to bother anyone. One young man of Sophy's acquaintance is a snake in the grass, and Charles highly disapproves of him. Miss Wraxton's younger brother is said to have made inappropriate advances on Cecilia, Charles' sister; Charles' reaction is very creditable.
Some of Sophy's plans include flirtation and something that looks like elopement.
Crude or Profane Language or Content
Characters frequently take God's name in vain ("Good God," etc.). "D*mn" is used occasionally, and "devilish."
"The Grand Sophy" is the first Georgette Heyer novel I've read, and I thoroughly enjoyed it. Some liken it to Jane Austen's novels, but the only similarity is in their both being set in Regency England: the writing styles and characters are vastly different. From the moment the titular character enters the scene, "The Grand Sophy" makes for a light, fun, fast-paced romance that, for all (or because of all) its quirks, also manages to be heartwarming. The characters stand out with originality and charm, especially the conniving but well-meaning heroine and the sharp-tempered, one-of-a-kind hero. The ride is never dull, though it is often agonizing, and the only problem with the ending is that it means the book is over.
Note again that this is not a Jane Austen novel, and Heyer does chip off some varnish to let the facts of the Regency Era show through. The dalliances of many of the higher-class men are mentioned and little to no judgment is passed on them. There is also the swearing mentioned above; the taking of God's name in vain is probably the weakest link in my enjoyment of the story and might off-put others even more. However, through such details as these Heyer envelops the reader in the world of the story. She knew what she was about when it came to the Regency Era, and the setting, the characters, and the plot are seamless.