Mortally weakened by the Spider Queen on Metebelis 3, the Doctor is forced to regenerate. His recuperation is cut short as UNIT investigates a spate of robberies involving components for a top-secret disintegrator gun. The culprit is quickly identified as a highly sophisticated robot built by Professor Kettlewell, which is being ordered to act against its Prime Directive. 1 2/3 hours on 1 disc. SDH