The Grand Sophy has always been one of Heyer's most popular books, and for good reasons. The main character, Sophy, is so confident, fun and extremely likeable - she is almost irresistable. It is also one of Heyer's more complex plots with a number of problems, mostly romantic to be resolved - and it is only in the last few pages that all is made clear.
Sophy, the 'little' neice of Lady Ombersley is sent to London to stay with her aunt. However, somewhere in the decade or so since her aunt last saw her, Sophy has grown into a rather tall, imposing woman, with a personality to match. She is good-natured, sociable, and utterly independent. She soon has the Ombersley household in the palm of her hand - well all except Charles, the eldest son who takes a rather dim view of her. Charles's pious fiancee, Eugenia Wraxton, is also not impressed by her and attempts to bring her into line with London manners - but Sophy, with unimpaired good-manners and immense charm usually manages to get her own way.
Having established herself in the Ombersley Household Sophy soon sees how much they need her. Charles is clearly about marry the wrong woman (Eugenia), his sister, Cecilia is caught up with a clearly unsuitbale poet, and younger brother has Hubert trapped in some clearly dark sort of activity which he cannot escape from. At the same time Sophy's soon to be mother-in-law, Sancia looks to be straying herself.
Sophy's ability to orchestrate this huge cast of characters all to fitting ends is truly marvellous - and highly enjoyable.