in 1975 creating his own science-fiction show, Survivors (1975–77). Survivors was a post-apocalyptic tale of a small group of people who were the only humans left after a plague caused by biological warfare lab accident has wiped out most of humanity. It ran for three seasons and was generally well received. Nation followed it by creating Blake's 7 (1978–81). Pitched by Nation as "the Dirty Dozen in space", Blake's 7 originally revolved around righteous freedom fighter Roj Blake, his battle with a corrupt Galactic Federation and the rag-tag group of pirates, criminals and smugglers who are reluctantly forced to work with him after an escape from a prison ship. Running for four seasons, the early evening series had a hard edge. The moral ambiguity of the leading characters made them interesting, and as with Doomwatch it was not afraid of shocking the audience by killing off leading characters, climaxing by wiping out the entire crew in its final episode. ITV was continuing to produce science fiction in this era. Keen to catch some of the young audience who followed Doctor Who, some of the ITV companies sought to create their own youth-oriented genre programmes, such as the 1970's cult classic sci-fi drama series, Timeslip (1970), and the original The Tomorrow People (1973–79). Although it presented some intriguing (if bizarre) storylines, it never rivalled Doctor Who, possibly because unlike the BBC programme it attempted to identify with children by featuring children, thus making the crossover appeal to an adult audience much more difficult. A much more respected show, produced by ATV in a similar production manner to Doctor Who (i.e. on videotape using a serial form) was Sapphire & Steel (1979–82). The tale of two "time detectives" played by David McCallum and Joanna Lumley, Sapphire & Steel was a superbly atmospheric piece of television, although its production run was often hampered by the unavailability of its two leads. 1980s Longer-running science-fiction series became few and far between. Although Doctor Who was still running, in terms of audience it was struggling to compete with US imports in the genre which began to re-emerge following the box-office success of contemporary films like the Star Wars franchise. For the television channel controllers, these had the benefit of transmission rights having a lower cost than any domestic productions. Dr Who's place in the Saturday schedule was briefly lost when it was moved to a weekday