Sam Abramski and his mother Rebecca join the local community to stop the British Fascists marching through London’s East End in 1936.
Inspired by the experience and against his mother’s wishes, Sam leaves home for the first time to fight with the International Brigades, helping to defend the newly elected Republican Government in Spain against the fascist military coup.
On the way to Spain, Sam meets Jack, who fought in the Great war and is older and apparently more cynical, and George, a more pragmatic volunteer who keeps up morale with his good humour and unshakable conviction.
Trapped in a failing marriage, Rebecca misses Sammy so much she decides to follow him to Spain to find him.
She joins one of the medical teams working as a nurse whilst searching for her son and meets Ernesto, a Spanish anarchist. Sammy meanwhile has met 18 year old Pilar, who has lost both parents and is trying to survive in war torn Barcelona.
After the hospital is bombed, Rebecca and Ernesto seek shelter at a convent where Ernesto’s sister is a nun.
When the local Loyalists’ militia discover she has sheltered them they kill her in cold blood. Ernesto and Rebecca escape and hide and Rebecca reveals that she is pregnant with Ernesto’s baby.
Jack, George and Sammy, still unaware of his mother’s presence in Spain, continue the fight even as the war is being lost. Sammy’s relationship with Pilar blossoms despite the war around them and they finally make love before Sam returns to the front.
As they become immersed in the ongoing battle, the musical takes the audience on an emotional rollercoaster ride as Sam discovers aspects of himself that he might otherwise never have known. Before reaching the final climactic scene, each of the characters has been profoundly changed by their extraordinary experiences which they can never forget.