The only Doctor Who in which The Doctor and his companions do not appear.
This episode takes place on Kembel in 4000.
In the original script, the Varga plants were natural, indigenous form of life. When the planet of the setting was change to Kembel, they became creations of the Daleks.
Terry Nation wrote this episode partially as an attempt to develop and sell the idea of a Dalek television series divorced from the larger Doctor Who (1963) universe. The proposed series would have followed the adventures of the Space Security Service, an elite organisation tasked with hunting Daleks. This approach can be seen in short stories and comic strips written for 1965's The Dalek Outer Space Book (cover dated 1966). An unmade pilot titled "The Destroyers" was written, but the series concept was never sold.
This episode was recreated by students of the University of Central Lancashire and streamed on YouTube on October 9, 2019, the 54th anniversary of the original broadcast.