When a patient wakes up after a tumour removal operation and displays a severe change in personality, the resident psychiatrist is perplexed - until Hartman's tumour is diagnosed, a rare condition that leaves its victims deranged and hospitalised in mental institutions. The patient's vindictive husband blames the neurosurgeon responsible for the operation, John Macandrew, and seeks cruel revenge. Macandrew retreats to his native Scotland and makes further discoveries about the mysterious illness, but the sinister biblical scholar Dom Ignatius already knows the secret and is wilfully ruining lives to achieve his own selfish aims. Worse still, he's determined not to let anyone stand in his way.