Sarah Waters hit the mainstream big time with The Little Stranger a few years ago, but she was already a superstar among lesbians and historical fiction buffs for her novels depicting gay and lesbian life in England.
Her first novel, Tipping the Velvet, is a picaresque tale that combines Charles Dickens with Henry Fielding. Sheltered Nan falls in love with Kitty, a male impersonator, and follows her to London, where she joins the act. After falling out with Kitty over their mutual feelings, Nan has many adventures and misadventures until she finds her true love in Florence, a socialist activist.
Affinity finds Margaret Prior, a "Lady Visitor" at a Victorian prison, entranced by Selina Dawes, a medium imprisioned there after a seance gone tragically awry. Margaret plots their escape after realizing their shared passion.
Fingersmith is a more convoluted tale, involving two young women named Sue and Maud. One is highborn and one is low, but both are connected in this story of cross and double-cross, with enough twists and turns to keep any fan of Charles Dickens entertained.
The Night Watch tells its story in reverse order, starting in 1947 and ending in 1941. Kay, Julia, and Helen form a romantic triangle while Viv has an affair with an earnest married man. Duncan and Fraser have a relationship that starts in prison and turns into a triangle with Mr. Mundy.
All these books drip with historical detail (Waters has a degree in history and started writing Tipping the Velvet while finishing her doctoral thesis) that enhances the story instead of burying it: the characters are people of their time. The sex can be explicit, but it is based on real emotions. The plots keep you turning the pages late into the night, and you cheer for Waters' protagonists. Unlike novels by previous authors, Waters' characters don't run and live in the woods away from an oppressive society, but stay in urban environments and engage and subvert that society. The combination of these factors make these books good, old fashioned fun.