Fate
Fate is a central theme in the plot of the musical. Early on, Mrs. Lyons warns Mrs. Johnstone that according to superstition, twins separated at birth will cause each other's death if they meet in life. This ends up carrying an unsettling resonance throughout the story, as the two boys are drawn to each other, despite repeated warnings from their mothers. Despite all of the circumstances that pull them apart, they prove to be inseparable. Mrs. Lyons' premonition ends up coming true, as Mickey kills Eddie during a fit of jealous rage. The narrator ends the musical questioning whether or not it was fate or class that ultimately brought about Eddie and Mickey's tragic demise. While he does not ultimately make a definitive judgment one way or the other, the narrator seems to suggest that there is a supernatural element to the boys' intertwined destinies.
Nature Versus Nurture
The concept of nature versus nurture reappears throughout the musical. Mickey and Eddie are identical twins who are separated at birth and experience entirely different upbringings. Eddie grows up as an only child in a wealthy family and is given material comforts and numerous opportunities. Mickey grows up in a single-parent household and is constantly at odds with his cruel older brother. Eddie prospers in school and becomes a local politician, while Mickey is caught up in a life of petty crime and prescription-drug addiction. Still, the boys find themselves constantly caught up in each other's lives and, especially as children, find an instant kinship. The musical reveals the ways in which their upbringings alter their respective lives while still being unable to keep them apart.
Class
Class is another important theme in the play. Eddie and Mickey's diverging lives are shaped dramatically by their class differences. Eddie is able to do well in his studies and secure a well-paying job because of his comfortable economic status. In contrast, Mickey is forced into much more difficult circumstances. He takes a factory job to make a living for his family but then loses it during a recession. Desperate, Mickey turns to crime as an easy way to make money and takes part in a botched robbery. This lands him in prison and causes him severe mental trauma. While the play shows the mythic elements of the brothers' story, it also focuses on the profound impact of class. At the end of the play, the narrator wonders if it was ultimately class and not fate that caused the two brothers' tragic deaths.
Family
Family is also a major theme in the musical. The musical questions the idea of what a family really is. Mrs. Lyons says her husband does not want to adopt a child because he does not believe it can ever truly belong to its non-biological family. However, she becomes incredibly attached to Eddie when she adopts him, as does Mr. Lyons who is none the wiser about her deal with Mrs. Johnstone. At the same time, Eddie and Mickey are magnetically pulled to one another, and Mrs. Johnstone continues to feel an intense emotional bond with Eddie. The musical highlights how strong the bond between the brothers remains while also showing how families don't necessarily have one definitive structure.
Trauma
Trauma is also a prominent theme in the musical. After a robbery goes wrong, Sammy murders someone and Mickey is charged as an accessory to the crime. The combination of witnessing the murder and the time he spends in prison makes Mickey severely traumatized. He becomes addicted to the antidepressants he is prescribed after the fact, making him essentially incapable of leading a normal life. The play shows how this disturbing event and its terrible aftermath damage Mickey permanently.
Love
Love is another core theme in the musical. Both Eddie and Mickey are in love with Linda. Mickey is able to attract the attention of girls but is unable to acknowledge the growing romance between Linda and himself. Eddie chooses not to tell Linda how he feels and instead helps Mickey figure out what to say to Linda. Linda and Mickey end up getting married after Mickey gets Linda pregnant. Later, after Mickey is released from prison, he becomes increasingly paranoid that Linda is sleeping with Eddie, as they continue to have a close relationship. Ultimately, this causes him to chase down Eddie in a jealous rage. The play shows how love can curdle into jealousy, causing awful events to transpire.
Violence
Violence is a major thematic element in the musical. Early in the story, Mickey and his friend play violent games in the street, shooting toy guns at each other, as depicted in "Kids Game." Later, his brother Sammy, who has bullied Mickey for years, flashes a knife at a bus driver. Later, Sammy ends up killing someone during a robbery and going to prison. At the musical's conclusion, Mickey grabs a gun and heads to the courthouse to kill Eddie. Sammy and Mickey's narrative arcs show how an early relationship to violence can lead to increasingly large problems. Toy guns eventually become real guns, as the musical reveals how the play of children eventually grows into crimes with irreversible consequences.
