Blood Brothers tells the story of the Johnstone twins, Mickey and Eddie, brothers separated at birth who reunite and become friends in their childhood, unaware of their relation to each other or of the consequences their relationship will bring about.

At the start of the musical, working class woman Mrs. Johnstone learns she is pregnant with twins and confides in her employer Mrs. Lyons about her fears that she will not be able to support both children. Mrs. Lyons, a wealthy and deceitful woman unable to have children herself, persuades Mrs. Johnstone to give up one of her boys with the promise that she will raise him in the lap of luxury. But when Mrs. Lyons fires the mother in hopes of making Eddie all her own, she is unable to separate herself and Eddie from the Johnstone family or from the lies of the past, leading both families towards a tragic end.

The story is told through the narrator, who is presented as an especially pivotal character, a manifestation of one of the visible themes in Blood Brothers - the idea that life is a game. He treats the characters as players of his game, manipulating their lives and playing off their superstitious beliefs. The narrator is always visible on stage, acting as a Mephistophelean puppeteer of sorts who manipulates the lives and families of Mrs. Johnstone and Mrs. Lyons.

Blood Brothers also explores class differences and the gap between classes through the way both the sons and mothers choose to live their lives. Mrs. Johnstone and Mrs. Lyons are in two very different classes, yet they are unable to avoid each other because of the connection their sons share. The differences in lifestyle, values, and morals of the two families are stark yet subtly done.

The most prevalent theme is within the constant reference to Marilyn Monroe. In the opening song "Marilyn Monroe", Mrs. Johnstone tells of her carefree youth, comparing every aspect of her life to that of the blond bombshell. The song is reprised several times, and though the reference becomes a bit tiresome, its relevance is strong. Although beautiful and successful, Marilyn Monroe led a complex life and in many ways brought on her own destruction. Her memory is framed by her bitter end just as the story of the Johnstone twins is framed by the image of the two brothers lying dead on the floor. Seemingly every major player in Blood Brothers is a tragic figure, meeting their own end through their own tragic means.

Through interactions between the narrator and the characters, Blood Brothers reaches a quick but powerful climax which holds so much meaning in last words spoken and the placement of every character on stage. The show ends as it started with the Johnstone twins dead and the narrator reprising his opening soliloquy, "Did you ever hear about the Johnstone twins??"

Blood Brothers is a variation on an old theme - twin brothers parted at birth, but is also filled with raw emotion, deception.  Blood Brothers becomes a moving production that is sure to leave you thinking.