At U.N.I.T. HQ, the Third Doctor makes Christmas dinner for Liz and Sergeant Benton using his latest technological inventions. A red flash in the sky outside heralds a thick snowfall, and then a hole in the sky appears above the U.N.I.T. barracks. The Doctor, Liz and Benton take Bessie to investigate. The hole is a portal to another dimension, out of which has fallen a large, dead, alien arachnid. A beam of light shines out from the hole, searching the area, which then pulls all metallic items into the portal – including Bessie.