The story began to "pay off" the Divergent Universe arc by explaining things like the Interzone, the Kro'ka's motivations and fears, how a universe without time worked and the Divergence itself. From a production standpoint, it was notable for its highly complex sound design, which had to depict abstract environments, including the Doctor's own mind. It also afforded Paul McGann the chance to play three different versions of his Doctor, each primarily exhibiting what Charley called a "mode" of his character. Thus, the story had one Doctor that was a bit surly and paranoid, another that was bouncy and excitable and another that was more or less the "regular" Eighth Doctor.