I'm looking for the title and author of a story I read years ago. In short: a crack pair of investigators arrive on a planet. One is a high level esper.
They go about their business but notice some of the native populace are "afflicted" with a bright red growth in varying degrees. Some have only a tiny spot, on others it covers large areas of their bodies. The natives consider the tumor-like growths a "blessing" or status symbol.
I don't recall specifics but the pair discovers a cavern filled with the red tumors. The next day the esper has disappears. The remaining off-worlder searches for her and finally discovers the tumors are related to esper ability, and how much you are "afflicted" is directly proportional to your level of ability. In short his partner melded with or was consumed by the tumors, becoming one with the mass in the cavern.