"The Tryst" by Monique Roffey

An audio book.

First person PoV Jane, about 40, has arty friends who sleep around a bit. She has sex fantasies while with them. When a stranger (to her) Lila turns up in the pub, attracting the men, Jane invites her to come home with her and Bill. She and Bill (divorced woodworking husband of 2) have been celibate for 2 years, married for 3. She loves him without ever having been sexually attracted to him. She's given him a decorative egg each year. Their first 3 dates are described.

Then we get Lila's first person PoV. Her pointy ears - a feature - come from her wood-nymph past (a past that may explain why she and Bill get on - Bill's the first man to excite her). She stays the night with Bill. She's thinking of "crossing over". She's learned sex tricks from whores through the centuries. Jane leaves the 2 of them to it. Lila thinks that Jane may have considered joining in.

We get Bill's PoV. He's besotted. Jane later returns to the house threatening Lila with a saucepan (Jane's read that imps fear iron). Lila goes. Jane goes. A few days later Jane returns, making love with Bill. She thinks she's part Lila, and Lila part her. And that's it.

Other reviews

• Jane Housham (Erotic literature is vulnerable to a number of stylistic weaknesses. It is, by its very nature, repetitive, while descriptions of sexual ecstasy can become unintentionally comic if they try too hard to convince the reader of the power of sex to transport. Happily, The Tryst is no contender for the Bad Sex award: the sexual descriptions walk the line between transcendent and plain dirty with perfect judgment.)
• goodreads