This partially runs alongside "The Making of a Valle". Though reading "The Making of a Valle" is not required to understand Sins of the Son, some stories do parallel.
With Dain banished and no longer wreaking havoc on the mortal and immortal, Emily and Chevalier return to life in Council City. While Emily sets out to find and free her young son from torment, Chevalier spends his time strengthening the Equites and attempting to protect Emily from the ever expanding threat from the unfactioned and the Valle.
Old friends reappear, but trust is hard to accept. Emily tries to follow the wishes of the faction and her husband, but emotions fight against what she’s struggling to do. Thoughts of loved ones and friends buried beneath the cold ground fill her mind at all times, and Chevalier thinks she’s in the need of a good distraction.
The faction and Emily learn more about Chevalier’s sordid past, when old enemies begin to seek vengeance against long-held grudges.