Historian Dan Snow and actress Natalie Cassidy set off down very different paths to try and discover the truth behind their families' roles in the Great War. Natalie's journey tracks some of the forgotten stories of the war and takes her from the bombed out streets of London to the mass burial sites of Belgium. Dan retraces the footsteps of his great grandfather General Thomas Snow and is shocked to discover that he may have been partially to blame for the slaughter at the Battle of the Somme.

• Kate Silverton
• Kirsty Wark