"Story arc" is a term which refers to a common thread in a series of stories, forming an overall "arc" throughout them. This can be a central subject that holds the stories together, such as Season 16 of Doctor Who, which featured the central theme throughout the season of the hunt for the Key to Time, or something less defined.
Throughout the novels published by Virgin Publishing and BBC Books, each of the main ranges featuring the Seventh Doctor and Eighth Doctor (respectively) had ongoing story arcs. During the Virgin New Adventures' first four novels, a common thread of a being known as the Timewyrm flowed throughout the first four novels. This story arc was also created as a marketing vehicle to lure new readers into the series.[source needed] The second series of novels, which purported to also be a story arc, was only very tenuously linked by its title, Cat's Cradle and the presence of a silver cat. This was far more a marketing ploy than a defined story arc.[source needed]
Throughout the Virgin New Adventures there were several story arcs that grouped several novels around ideas that flowed through sets of novels. The novels Blood Heat, The Dimension Riders, The Left-Handed Hummingbird, Conundrum and No Future had a common idea and a central character revealed only in the final novel of the story arc as the individual responsible for events throughout the arc.
When Doctor Who was revived for television by BBC Wales, Russell T Davies, the show's executive producer and head writer, introduced the first story arc for the new series of Doctor Who, known now as the Bad Wolf arc. It was the defined story arc which appeared throughout the first series of BBC Wales' Doctor Who.
The story arc has become a common feature of the new televised Doctor Who, with each series revealing its own unique story arc carried throughout each series.