While the core cast does not change throughout each individual series, there are various guest cast and characters. Please see individual story pages for more detail.
Colonel Chaudhry is the only character to appear in all five audio dramas in the first series.
Brigadier Lethbridge-Stewart is the only character from the classic series to appear in UNIT.
Unusually, the end of each episode of the first series closes with a next time trailer narrated by Nicholas Briggs. This would not become common practice until the new series began airing on television.