Karon's books are truly about the Christian principles of grace, love and redemption and about perfecting the ability to forgive. But, if there is a dark theme in her books that theme is from Exodus 34:7 where it says, "visiting the iniquity of the fathers up on the children... unto the third and to the fourth generations."
Father Tim spends an inner lifetime trying to understand his father, wondering why he never received or could earn his love, praying for his father and looking for grace to have touched his life. What he finds is a terrible incident that left an emotional scar in his father's life that did not heal and tormented his grandparents, mother and self even beyond his father's passing. While he doesn't understand, he tries to empathize and to forgive and to find peace.