 Episodes 5 and 6 were originally to have been written by another  writer. However when early drafts proved unsatisfactory, the writer  was fired and Russell T Davies (qv) elected to write the entire  series himself. As a result of this, episodes 5 and 6 were written  after episode 7 (but before episode 8) and were somewhat lacking in  plot. Davies has never revealed which writer let them down.