When the Daleks probe The Doctor's mind, we see clips of every past Doctor and companion, with the exception of Leela, as she was accidentally omitted. A photograph of Katarina from The Dalek's Masterplan is used, as no clips of her were thought to have survived.
Tegan comments that the cylinders are very lightweight. Later, two Dalek Troopers carry one cylinder between them. This is not an error in depicting the weight but rather reflective of the care they are giving to the canister's contents: it contains the Movellan virus which is deadly to their Dalek masters who are also present. Unlike Tegan's haphazard handling, they are taking care to keep it level and not bang it around.
Director Matthew Robinson planned to record the final battle sequence using multi-camera technique, which was the normal way of recording at Television Centre, but ran out of time and had to resort to using single-camera because multi-camera would have required rehearsal.
Writer Eric Saward was dissatisfied with his own story, later saying that it was too frantic, with too many ideas, and he regretted the excessive body count. The main plot was the Daleks releasing Davros so he might find a cure for the Movellan virus. There were several sub-plots: the creation of duplicates to invade the Earth; the capture of the Doctor to create a clone to assassinate the Time Lords' High Council; and Davros' scheme to create a new race of Daleks. As none of these are dealt with at any length, he felt they distracted from the central plot. However, Peter Davison said he liked the script and thought this story was one of the highlights of his final season.
This episode was watched by 8 million viewers on its original transmission.