Terrance Dicks, who had worked on the series as a script editor since 1968, was also leaving, to be replaced by Robert Holmes. Holmes had been a writer for the show since season six and penned four stories in Pertwee's era, including "Spearhead from Space" (1970), the Third Doctor's first serial. Though Dicks was leaving as script editor, he would still be involved with the series as an occasional writer. Having previously helped write the serials "The Seeds of Death" and "The War Games" (both 1969), Dicks would write the first story for the incoming Fourth Doctor.