Book excerpt: When Ross Heaven, a psychologist and ex-pharmaceutical industry consultant, embarks on a shamanic apprenticeship in the rainforests and mountains of South America his intention is to unlock the secrets of San Pedro, the mescaline cactus that has been used as a sacrament and teacher plant in Peru for millennia, and to learn about love and healing. What he finds is more remarkable, painful, enriching, liberating and extraordinary than he could have imagined. ,