This story was originally intended to be a crossover with the modern Doctor Who series; Russell T Davies, an executive producer of Doctor Who and creator of The Sarah Jane Adventures reveals in his non-fiction book Doctor Who: The Writer's Tale that former companion Martha Jones was intended to appear in the two-parter, but had to be replaced with classic series character Brigadier Lethbridge-Stewart (Nicholas Courtney) "at the last minute" due to Freema Agyeman's role in the ITV series Law & Order: UK,[1] making this the last episode to have Courtney as the Brigadier prior to his death in 2011.
[N 1] She is searching for the body of Horath, an immortal cyborg that was defeated and had its consciousness separated and placed at opposite ends of the galaxy 3,000 years ago.
[N 2] Aided by Sarah Jane's old friend, Brigadier Lethbridge-Stewart, Sarah Jane and Rani sneak into the UNIT Black Archive, a secure storehouse of alien artefacts, to get the Tunguska scroll, which can find the Neolithic stone circle leading to the dimension where the body of Horath is kept.
Wormwood forces Luke to enter and place the scroll on the central stone, which opens the portal to the dimension where the body of Horath is located.
Brigadier Lethbridge-Stewart last appeared in the Doctor Who serial Battlefield, although he had a brief cameo in the charity special Dimensions in Time.