The film was released on YouTube at 5:50pm GMT on October 9, 2019, exactly 54 years to the minute after the original episode Mission to the Unknown (1965) was shown on BBC One.
The film was introduced by Edward de Souza, who played Marc Cory in Mission to the Unknown (1965). He and Peter Purves, who played the First Doctor's companion Steven Taylor from 1965 to 1966, visited the set during filming in February 2019.
The film takes place on Kembel in 4000.