It is September 1940. The constant nightly bombing by the Luftwaffe has set London ablaze. The city is in chaos. Together with polio survivor Ella (14), you see how ‘every evening the sun seems to set on the wrong side’ and ‘the eastern sky glows a fiery orange’. You smell what is happening as the port and warehouses go up in flames, and you can feel the threat of the unexploded bombs. ‘The world seems to be made of glass. One wrong movement and everything will collapse,’ says Ella, already literally and figuratively thrown off balance by her polio-damaged leg. At night, she hides out in the Underground with her brother Robbie, in a deep tunnel. They are joined by the opportunistic street kid Jay, and later by the free-spirited Quin, who has fled her aristocratic existence, and her brother Sebastian. Their common fate proves stronger than their apparent class differences, and a tentative friendship grows between them, one that will define their lives.

The threat of war and the claustrophobic conditions underground cleverly take on a double meaning when it turns out that, as a polio patient, Ella had to lie in a tunnel-shaped breathing machine in order to survive. ‘Breathing isn’t something you can practise,’ she says. ‘There is no shallow water, no summer’s day without Messerschmitts. If you get it wrong, you’re a goner.’ The prologue already reveals that one of the friends will die – but which one will it be?

The war gets the adrenaline pumping and makes Ella unexpectedly courageous. The air-raid siren howls ominously, but ever since she tore up her storybook full of adolescent ‘foolish hot-air balloons’ and Quinn taught her that ‘the world is bigger than our parents think’, she no longer wants to wait passively. She may have a limp, but she can choose: ‘I want to know what’s coming next. And soon. And tomorrow.’ The adventure that follows leaves an indelible impression.