1916, and Britain's armed forces are decimated. Across the country, friends join up to fight together, in new battalions known as 'Pals'. Paddy Kennedy, a warehouse clerk from Manchester, joins the Manchester Pals Battalion alongside his friends Henry, Andy and Jim. They soon discover that the whole of their neighbourhood has joined up, including a nearby factory foreman, now their sergeant, Mitchell and their friend Lizzie, who has become a volunteer nurse. These pals are set to become part of the largest offensive ever mounted by the British Army, the Battle of the Somme. But after a successful first day, they are ordered to seize control of Trones Wood, a thickly forested copse riddled with enemy soldiers and impossible to navigate. Through all this, they survive shellfire and ambush, evade capture by the Germans and encounter the mysterious Private William Hunt, whose fate will become forever entwined with the life of Paddy Kennedy. Paddy's journey leads to the deadliest mission of all - the execution by firing squad of one of his pals. How will Paddy survive becoming a soldier?

1918, and after four years of combat the British invent a new weapon designed to break the stalemate. Private Chas Rowland, determined to bring the war to an end and return home, joins the Tank Corps under the command of Lieutenant Mould, entering the extraordinary world of the Niveleur, a Mark V tank. Primed to take part in a major offensive against the Germans just outside the French town of Amiens, the crew of the Niveleur include Fred Firth, a father-of-two desperate to see his children again; Private Dodds, a tough warrior scarred by the loss of his brothers; and Mike Weston, a civilian mechanic conscripted into the tanks. The crew will only survive four gruelling days behind enemy lines if they can learn to work together. Can they bring the war to an end and make it home?