A song for Laya

A song for Leia by George R. R. Martin ... in the distant future, in a time when humans spread across the galaxy and traveled between stars and met different creatures from other worlds, a human settlement is established on a newly discovered planet, inhabited by simple peaceful people who still live in their primitive era for thousands of years, and all believe in one religion. The Eshkin welcome the humans warmly and allow them to live among them, but it is soon discovered that their religion involves a very strange kind of suicide, which they accept at the end of their lives with joy and courage, and this prompts the human leadership to summon the two investigators with extraordinary psychic abilities, Rob and Liana, to answer a very dangerous question: why did humans themselves start adopting that mysterious alien religion?