The Black Moon is the fifth novel in Winston Graham's sweeping series of Cornwall, Poldark. Cornwall 1794. The birth of a son to Elizabeth and George Warleggan serves only to accentuate the rift between the Poldark and Warleggan families. And when Morwenna Chynoweth, now governess to Elizabeth's eldest son, grows to love Drake Carne, Demelza's brother, the enduring rivalry between George and Ross finds a new focus for bitter enmity and conflict.

(From Goodreads)