out of five, contrasting it with the Philip Hinchcliffe era and describing it as "a kidified, Poundland Star Wars". He felt "many of the effects are excellent" but observed a "precarious juxtaposition" between good and bad effects and "the ambition of the serial as a whole". He praised the story as a "romping yarn" which "brings out the best in veteran designer Barry Newbery", but criticised "unbelievably incompetent" action scenes, as well as "harsh lighting" and "pristine white sets". He also commented on Louise Jameson as looking "unsurprisingly ill at ease" despite giving "her usual 100 per cent". DVD Talk's John Sinnott disliked the way K9 was used too conveniently and found the plot too similar to Fantastic Voyage (1966), but less well done. He praised the visual effects of the inside of the Doctor's head, but criticised the other sets. Commercial Releases In print A novelisation of this serial, written by Terrance Dicks, was published by Target Books in March 1979. Home media The story was released on VHS in September 2002. The DVD was released on 16 June 2008 with the spin-off "K-9 and Company" in a double pack called "K9 Tales". This serial was scheduled to be released as part of the Doctor Who DVD Files in issue 133 on 5 February 2014. References External links Target novelisation On Target — Doctor Who and the Invisible Enemy Fourth Doctor serials Television episodes about cloning Fiction about size change Fiction set on Titan (moon) Doctor Who serials novelised by Terrance Dicks 1977 British television episodes Television episodes written by Bob Baker (scriptwriter) Fiction set in the 5th millennium Television episodes set in hospitals