The third part of the Highland wildlife saga narrated by Ewan McGregor. It's a still, clear autumn day in Glen Affric in the north west Highlands. The forests are flushed with gold, but it's a shallow beauty that marks the beginning of the Highlands' longest, darkest and most overwhelming season. Animals that can't migrate to milder climes have to be equipped to deal with an all-out assault from the weather. Reindeer, ptarmigan and mountain hare are all adapted for these arctic-like conditions, but this turns out to be one of the snowiest winters in living memory, driving the animals of the Highlands to the absolute limit.

• Ewan McGregor