It is 1956 and a virus has wiped out the crops of South East Asia, causing a famine.
John Custance and his family visit his brother David's farm in Westmorland, convinced that the same thing could not happen there.
The world begins to panic as the virus spreads.
But just as things seem to be calming down a little, Roger confronts John with some horrifying news.
Having broken past the roadblocks, the convoy is hoping for a clear run to Blind Gill.
But a level crossing, a gatehouse and a carjack change the Custances's lives for ever.
The journey to Blind Gill continues, with one addition to the group and one sudden, shocking loss.
Both events shed new light on the increasingly disturbing behaviour of Mr Pirrie.
The end of the journey is in sight but there are still plenty of obstacles ahead.
At the last of them, John has to make an agonising choice.