“The Vale of Lost Women” takes place after the events of “Queen of the Black Coast” and Belit's death. Conan has joined the Bamula tribe in the jungles of Kush, becoming their new tribal king. In an effort to propose a possible truce, Conan visits a rival tribe called The Bakalah. It is here that he meets a white female prisoner named Livia. He learns that both Livia, and her brother, are scientists from Ophir that were captured by Bakalah warriors. Livia's brother was tortured to death, and she's certainly next to die.
Livia suggests to Conan that she is a virgin, and after he refuses to free her, she offers him her body. Conan then agrees to help her escape. Later that day, she sees Conan walking towards her carrying the bloody severed head of the Bakalah's tribal chief. In fear that Conan, now drenched in crimson, is coming for her, she escapes on horseback into the jungle. It's this portion of the story where things take a bizarre turn.
Livia falls from her horse and discovers she's in a beautiful valley that is home to a tribe of black lesbians! But, the lesbians are using poisonous orchids to create a hallucinogenic effect, placing Livia in a trance. She finds that these lesbians are sacrificing her on an alter to a giant black bat! Thankfully, Conan has trailed Livia and fights off the giant bat thing. Livia, fearing that Conan will attempt to claim her, becomes frightened. However, Conan simply advises her that he made a mistake in accepting her proposal to give herself to him. Arguably, he is suggesting there is no honor in that. Instead, he agrees to guide her to the Stygian border where she can eventually find passage to Ophir.
There isn't much to Howard's story, which probably contributes to the possibility that it was never submitted for publication during the author's lifetime. The imagery of Conan slowly walking through carnage holding a severed head is memorable, but aside from that there isn't a whole lot to highlight. But, the story does present a rarely seen moment of the hero's life as the Bamula leader.
Besides “The Vale of Lost Women”, Lin Carter and L. Sprague de Camp authored a 1969 story called “The Castle of Terror” that briefly recaps Conan's tenure with the Bamulas, stating he ruled the tribe for a year. It further states that a severe drought struck the region of Kush, which the Bamulas blamed on Conan, ultimately forcing him into exile. Roland Green's 1994 novel Conan at the Demon Gate also depicts Conan's time with the Bamulas and his rise to ruler of the tribe. Marvel's Conan the Barbarian adapted events from “The Vale of Lost Women” in issues #101-104.
Personally, I feel that artist Ken Kelly's cover art for Conan the Bold, a 1989 paperback by John Maddox Roberts, is a good recommendation of Conan battling a "bat creature" while protecting a girl, an event that happens in "The Vale of Lost Women" but oddly never occurs in Roberts' novel. Also, Conan battles a "dark bat thing" while protecting a girl in Conan the Barbarian #9, an adaptation of Howard's 1934 horror story "Garden of Fear". Both Kelly's artwork for the novel and Roy Thomas's writing in the comic just remind me of "The Vale of Lost Women" for some reason.