Kathy as an allegory for drug addiction
Kathy's story offers an alternative narrative for talking about drug addiction. By honoring her legacy, MacDonald highlights the tragedy of her situation, a young, impressionable girl constantly exposed to bad company who finally succumbs to a temptation once and ends up hooked. Instead of showing Kathy as a criminal, we see a Kathy who is permanently disabled by a few serious mistakes. Perhaps with more stability, more resources, and sense of hope for a better life, Kathy might have recovered, but there is simply nothing in her world that helps her feel happy like drugs do. Her case is another instance of mental health combined with drug abuse.
Davey's story as an allegory for mental health issues
Another archetypal character is MacDonald's brother Davey, who like Kathy is not portrayed as a hopeless nut, but rather as a complex, struggling person with a serious affliction. Again, perhaps with more stability, better resources, and a hope for a better life, perhaps Davey could have learned how to live a healthy, balanced life with schizophrenia through treatment and medication. Instead he falls victim to the hopelessness of his situation and ends it all in an act of suicidal depression. It is not because he is evil that he dies, but rather because his chances at a healthy, hopeful life are so slim in a community like Southie.
Kevin and Frankie as an allegory for family and loyalty
One of the greatest acts of loyalty is when Frankie protects his brother Kevin by taking the fall for Kevin's drugs. Unfortunately, this qualifies him for criminal loyalty, and Frankie's decisive, selfless qualities end up being his downfall when he encounters Whitey's gang who are way more than willing to make use of such a loyalty. Kevin is also an instance of this, and although they Kevin never indicates it, there is a sense in which Frankie's death propels him toward suicide. Ultimately, the commitment to brotherhood and family kept him alive in the criminal element, and without it, Kevin finds himself without a reason to live.
MacDonald as an allegory for survival and hope
MacDonald himself exists within a type, the archetypal hero who leaves his family behind to gain new experiences and then returns home again. This return is the reason for his telling of the story, because it represents the completion of his cycle.
Whitey as a symbolic character for criminal power
Instead of depicting the criminal element as a healthy part of the community, MacDonald is careful to tie his family's downfall to the evil forces of Whitey, whose willingness to exploit needy and struggling people leads him to adopt several brothers into the gang, and causes drug addictions to fuel his power.
