sentences:  By late April 1968, it was clear that Frazer Hines would be leaving the series sometime during Season Six.One candidate for his departure story was Haisman and Lincoln's third Yeti serial, which they were working on around the start of June.Over the summer, however, the writers became embroiled in a dispute over copyright with the BBC regarding the Quarks, robot monsters which had appeared in their previous "Doctor Who" commission, "The Dominators".