Through the Third Eye (Third Eye Trilogy Book 1) - Bob Frank

Clay Barton gained access to temporarily declassified past life regression protocols used by the CIA when he worked at the Stanford Research Institute. Since then he has been something of an armchair treasure hunter, conducting hypnotic past life regressions on people.
Shali Faisal and Clay take their roaming reincarnation parapsychology practice direct to their subjects and guide them through their past lives. They coax out information about lost valuables or hidden treasures from long ago. The subjects remember almost nothing of their reincarnation sessions so the rewards are all theirs for the taking.
They heard whispers about a collection of “hidden writings” that have ties to the rumored secrets of the universe. Upon finally finding these treasures, they are confronted by a unidentifiable, secretive nemesis intent on stopping them. Despite being aided by a benevolent ally, they are repeatedly blocked from their goal.