Father's Day was one of the highlights of the first series of the rebooted Doctor Who, dealing with the very dramatic consequences of Rose changing her own personal history by saving her father. Ignoring the Doctor's warnings, Rose's actions resulted in Reapers - giant dragon-like creatures - becoming unleashed on humanity as a result of altering time. The moral dilemmas and indeed the threat of the Reapers made for a powerful story. The only trouble is they have never been seen since and technically should appeared many times throughout the Doctor's long history. History has been changed on numerous occasions but the Reapers remain silent, begging the question; why were they there at that point in particular? Doctor Who has dealt with the consequences of altering time on many occasions - perhaps most dramatically in The Wedding Of River Song. However the Reapers have been quietly forgotten about, making their one off appearance a little odd.