The World of Ptavvs (Known Space)

Larry Greenberg's telepathic tendencies had been trained and developed to a critical level. The trouble was that if these psychic interchanges were strong enough, a man could end up not knowing who he really was. And when Larry's mind is taken over by a sinister alien force, he has to fight to retain his sanity - and divert a disaster that threatens all mankind...

"Snappy, ingenious, and upbeat." - Galaxy

Made the 1st ballot for the 1967 Nebula