On the coast of Cornwall, the boy Philip Ashley is raised by his older and wealthy cousin Ambrose on a large estate. When the weather in Cornwall threatens Ambrose's health, he leaves the estate for a warmer climate, making his way to Florence and leaving Philip behind with his godfather, Nick Kendall. In Florence, Ambrose decides to marry his cousin Rachel. However, back in Cornwall, Philip receives disturbing letters from Ambrose, complaining of Rachel's treatment as well as that of the physicians taking care of him. Mr. Kendall believes Ambrose unsound of mind, raising the possibility that he has inherited his deceased father's brain tumour. When Philip travels to Florence personally, he meets a man named Guido Rainaldi, who tells him Ambrose has died of a brain tumour, producing a death certificate as proof, and that his will left the Cornwall estate to him upon his 25th birthday. Rachel, who left Florence the day before Philip arrived, has inherited nothing and has made no claim on the estate. Unconvinced, Philip suspects Rachel of murder and vows revenge.