The first key theme, that of self-forgiveness and acceptance, is made extremely clear by the end of the novel. The protagonist, Cadence, having lost her memory in an accident two years prior, finally recalls that her beloved cousins passed away in that same accident. She struggles not only to grieve their loss but also to forgive herself, as the situation that led to their deaths was an idea she conceived. Through an experience with either the spirits of her passed cousins or hallucinations of them, Cadence is assured that they do not hold her responsible for their deaths. Through this, Cadence is able to begin accepting the reality that they are gone, and she is also able to begin giving herself grace for her mistakes. The novel also highlights the necessity of this forgiveness. It does not downplay her grief nor her part in the tragedy. Instead, it recognizes that this self-acceptance is vital. The past cannot be changed, but people certainly can. Cadence undergoes a major transformation upon learning the truth about Summer Fifteen, one that centers around her grappling with her guilt.

The dangers of privilege and power are demonstrated by the actions of Cadence's family members. She comes from a wealthy family, and her grandfather, Harris, is the patriarch of this family. His three daughters, Cadence's mother and two aunts, are grown, well-educated women and yet still fully dependent on their father and unable to support themselves. Cadence and her cousins continually witness their mothers arguing over things such as their inheritances and the value of their father's property. The children detest this arguing and see it as tearing their family apart. The family’s reliance on wealth and prestige lead to the arguments that prompted the fire, ultimately leading to the Liars' demise and Cadence’s injury. This privilege contributed to both bickering and a serious tragedy. The Liars had a sense of power instilled in them by their privilege that was misplaced: clearly, burning a house down is a poor solution.

An important theme throughout the novel is the role of memory. Most notably, Cadence loses her memory of Summer Fifteen after her somewhat mysterious head injury. She spends two years with only a vague understanding of what transpired that fateful summer. When she returns, her disappointment and confusion is palpable: everything seems different. The biggest twist in the novel—that the Gat, Johnny, and Mirren she’s been talking with are ghosts or hallucinations—involves Cadence’s perception. The audience, too, is left trying to piece together what happened: reality has shifted. Cadence’s reality felt off and altered because it was inaccurate. There were pieces missing, both from her injury and from her absence the summer prior. Her grandfather also struggles with memory. Once the revered patriarch and figurehead of the family, Harris Sinclair now suffers from dementia. His historic home has been remodeled into a cold, modern abode that is unfamiliar to Cadence. Her memories and expectations have been jarred against the difficult reality.