Derry: ground zero for the outbreak of conflict in Northern Ireland. Is it once again being threatened with instability as Brexit causes deep uncertainty over the border? Naomi and Tim travel north just as unrest breaks out in the ancient city as Protestants and unionists prepare to mark the 12th of July: a yearly celebration of their culture. We chat to a man who lost his father in Bloody Sunday, speak to children building a bonfire about why they burn the Irish flag, and sketch out why this city of so much promise has been held back by decades of discrimination.