Mission to the Unknown is a noteworthy Doctor Who story for several reasons. Firstly, it marked the end of the reign of Verity Lambert, the show's original producer. Secondly, it was the only story, apart from the 1983 hour-and-a-half special "The Five Doctors", to be just one episode in length. And most importantly, it is the only Doctor Who episode to feature neither the Doctor nor any of the companions!

The episode serves merely as a teaser for the epic twelve-parter "The Daleks' Masterplan", which would follow a month later. No announcement was made before or after the broadcast about the non-appearance of the regular TARDIS crew, so this must have come as a surprise to viewers. In addition, the following week would see the TARDIS land near ancient Troy for "The Myth Makers", a story totally unconnected to the events of Mission to the Unknown. Thus the surprise would have been maintained when the TARDIS finally arrived on Kembel fully 5 weeks later.

Mission was broadcast in late 1965, and can count among its influences the early James Bond films... look out for the immortal line "Space Security Service - Licenced to Kill"!!