"Somewhere in this polar waste, something pretty deadly to Earth is Hiding!"

Sub Zero - Episode 3

Time is running out for the Doctor and Lt. Davis, as the Daleks put the first stage of their plan to conquor the Earth into operation - first they Exterminate all life at the weather station, before torching the base itself, in order to prevent anyone using the station's radio equipment to send out a warning. As their plane returns to the base, the Doctor realise things have gone badly wrong, when they get no radio guidence from the base as they try to land in the encroaching blizzard... then they spot the base itself is ablaze.

Unable to find a safe place to land due to bad visibility, Davis is forced to crash the plane into a snowdrift when the fuel runs out. The two stagger from the wreckage, fortunately alive, but with nowhere to go for shelter. The Doctor decides the only option is to follow the tracks left by the base's attackers - they set off as the blizzard begins to worsen... will they make it alive?