To mark the 90th anniversary of the end of the First World War, Tony Robinson travels to the Somme. When shelling turned the battlefield of the Somme into a hell on earth, Britain's best miners and engineers created a maze of tunnels and dugouts that would become the setting for a secret war waged underground. One of the last dugouts constructed has been drained of water, enabling the first people to enter it in 90 years. Deep beneath Flanders fields the skilled work of the elite tunnelling companies is revealed to be in a remarkable state of preservation, allowing Tony and the experts to walk into what effectively is a time capsule of the Great War.