When successful neurosurgeon John MacAndrews performs a routine operation to remove a tumor, the patient undergoes a severe personality change post-surgery. Hartman's tumor is diagnosed, a rare condition which leaves its victims deranged and destined to be confined to mental institutions. There is no option but to have the patient committed. With his career nearing ruin, MacAndrew retreats to his native Scotland to lick his wounds and it is there that he makes further discoveries about the mysterious illness and the chemical that induced it. MacAndrew thinks he may be able to save his patient, until he discovers someone is deliberately using the chemical to regress selected individuals and gain eyewitness accounts of events in the past.