Terrance Dicks worked together with Malcolm Hulke on scripts for The Avengers as well as other series before becoming Assistant, and later full Script Editor of Doctor Who from 1968. Dicks worked on the entirety of the Jon Pertwee Third Doctor era of the programme, and returned as a writer - scripting Tom Baker's first story as the Fourth Doctor: Robot. His later script writing credits on Doctor Who included the 20th anniversary story The Five Doctors. Terrance Dicks novelised many of the original Doctor Who stories for Target books, and has written original Doctor Who novels for BBC Books. Mervyn Haisman and Henry Lincoln worked together on scripts for various TV series in the 1960s, including Doctor Finlay's Casebook, Emergency Ward 10, and Doctor Who. Two of their Doctor Who scripts featured the Yeti - servants of an alien intelligence - which proved very popular and memorable. Haisman, who had previously been an actor, and managed a theatre company, continued to write television during the 1970s and 1980s. Lincoln, who had also been an actor under his real name of Henry Soskin, co-authored the book The Holy Blood and the Holy Grail.