Darkover is in danger. Alien forces are conspiring to ruin its economy and wipe out is ruling class. In desperation, nominal ruler of the planet Regis Hastur reaches across the universe for telepaths to train and enlist to their causes. His call for help somehow attracts a nonhuman from his own planet, a chieri from an ancient and superior race that is dying out of its own accord.
Still just six book into Bradley's monmouth series, and published in 1971, it's still massively sexist, with a female character getting branded a nympho, without much sympathy. The de-sexed lesbian and bisexual Free Amazon renunciates make their first appearance, but they don't get much page time. An intersex character is described as "passive" as he transitions to female, but there is an openness to sexual variance that is new to the series. Straight guys have sex with intersex characters, homosexuality is mostly viewed as okay, polyamory (or at least polysex) is acceptable, and there's a big old orgy scene toward the end!