Geologist Iain Stewart retraces the steps of a band of maverick pioneers who made ground-breaking discoveries in the landscape of Scotland about how our planet works.

In the final episode, Iain finds out about daredevil scientist Louis Agassiz, who first imagined the world had been gripped by an ice age. Plus, the story of humble janitor James Croll, who used the planets to work out the natural rhythms of the earth's climate.