As the novel's title strongly suggests, the traditions of stage drama and theatre, most particularly found in opera, are a key thematic concern of this text, most particularly in the way that characterisation is explored. This is made explicit at the very end of the fifth section of the novel, where Liesl explains to the narrator her theory on Dunstan's character and what role he plays, and how in particular he relates to the "Fifth Business," who relates to the other stock characters and produces the necessary element of drama through his interactions:
The prima donna and the tenor, the contralto and the basso, get all the best music and do all the spectacular things, but you cannot manage the plot without Fifth Business! It is not spectacular, but it is a good line of work, I can tell you, and those who play it sometimes have a career that outlasts the golden voices.
The theme of drama and theatre therefore relates to the title of the novel, and also the state of being "Fifth Business," which quite clearly is Dunstan's role in this novel and in the strange network of relationships he finds himself working within. In particular, Dunstan comes to explain his actions as to why he disclosed to Paul Dempster the secret behind his birth, and Boy Staunton's involvement in it, as being part of his role as "Fifth Business." He, as Liesl identifies, knows the secret of the hero's birth, and is, indirectly at least, the cause of Boy Staunton's death because of this revelation. Drama and theatre therefore lie at the very heart of this novel as the author uses this theme to develop role and character.