It's Christmas time again and the 'Pilot Fish' robots are back on Earth once more, disguised again, as killer Santas. This time they are under the control of a giant semi-humanoid arachnid from deep space. Called the Empress of the Racnoss, She is a half humanoid half spider creature intent on taking over the Earth for her own ends. Having travelled across half the Galaxy in her giant 'Webship' and with thousands of spiders at her command, even The Doctor may not be able to thwart her evil plans.