In this sixth book of the Poldark Saga, the four swans are four women whose lives touch Ross: Demelza, Elizabeth, Caroline, and Morwenna. For a man that often seems to be rather ignorant of love beyond his past pining for Elizabeth, Ross has a remarkable romantic streak for the lives and relationships of others! This story perhaps falls more in the "romance" genre than the others as numerous men reconcile themselves to loves they cannot have--Demelza's brothers Sam and Drake and the besotted Hugh Armitage, yearning for the wife of the man that saved his life.
The author includes many moments of introspection and deep thoughts in this novel. From Hugh: "By giving love you do not diminish it. Love only adds to itself, it never destroys. Tenderness is not like money; the more you give to one the more you have for others." From Ross: "No man wants his wife to be a woman that other men don't desire....But every man wants his wife to be a woman that other men don't get."
Intertwined in the lives of the characters (Ross, Demelza, George, Elizabeth, Drake, Sam, Dwight, Caroline, Morwenna, Osborne) is the ongoing Napoleonic war and civil unrest in England among the poor. The feud/competition between Ross and George continues and compels both men to take actions to try to best the other.