The Seeds of Death
In the serial , the time traveller the Second Doctor ( Patrick Troughton ) and his travelling companions Jamie McCrimmon ( Frazer Hines ) and Zoe Heriot ( Wendy Padbury ) , along with the technicians Gia Kelly ( Louise Pajo ) and Phipps ( Christopher Coll ) , try to prevent the Ice Warriors' plot to make the Earth's atmosphere inhospitable to humans but viable for the Ice Warriors to invade . 
<triplet> Second Doctor <subj> Patrick Troughton <obj> performer <triplet> Jamie McCrimmon <subj> Second Doctor <obj> sidekick of <subj> Frazer Hines <obj> performer <triplet> Zoe Heriot <subj> Wendy Padbury <obj> performer