There is a memorable quote in a recent Jordan Peterson lecture that frames this novel's premise quite well. Peterson comments in a lecture on Jung and The Lion King that after the terrorist attacks on 9/11, "The world wasn't sure what exactly fell." This novel takes that question as its thematic consideration, showing that the full change brought by the collapse of the Towers was felt in complex ways that are hard to define and which therefore warrant a novel's consideration.
There are several symbolic issues that cry out for interpretation. To name just two of them might give a helpful head-start. First, there is the broken relationship between Lianne and Keith in contrast to his blooming relationship to another Tower survivor, Florence. Secondly, there is the thematic consideration of memory and the past. In the first issue, Keith goes back to his old marriage, a marriage that was symbolically broken even before the attack (showing that the past isn't automatically healthy and good). He does this not because the past is worth returning to, but because he has to have some semblance of a life, and he uses the past as the framework for a new order in his life. This is symbolized by the fact that the paramedics drop him off at his ex-wife's house.
Not only is Keith defined by his relationship to the past, but he is also impacted by moving back in with a past wife. His wife's life is also defined symbolically by memory, past, and nostalgia. Lianne literally works with Alzheimer's patients who are afflicted with a biological impairment in their brain that limits their perception of the past. To quote another writer from this school of literature, Alzheimer's disease leaves patients in a perpetual experience of the "now" without reference to the past (this is Franzen's commentary from "My Father's Brain"). Together, these symbols capture the effect of the terrorist attacks. Instead of belonging in the present, the nation is left trying to remember what it felt like to be in the past, struggling to find health in that broken nostalgia.
