Daughter of Darkness — Herbert Grosshans

The Xandra: Book One Daughter Of The Dark By Herbert Grosshans -- In the 30th century humans are reaching out toward the far stars. Earth is sending huge ships carrying thousands of colonists in search of suitable planets. Nu-Eden, 325 light-years from Homeworld, looked like an ideal planet--until the colonists discover it is already occupied by a sentient entity who calls herself 'The Xandra', and she is not willing to share her planet with the humans. The colonists are beginning to behave strangely. At night they have sex-orgies, which they don't remember by day. Tom McClary loves his wife, Anina, but the lure of the Xandra may be stronger than his love for her. Even the space-station may not be safe from the influence of the Xandra.