When eccentric industrialist William Potts and his wife Mildred adopt Rosie, orphaned in a railway crash, they almost rue the day. Born in the East End, Rosie is pugnacious and difficult. But one summer day, standing on a Kentish hillside, she sees a kite rise high into the sky, and knows that in the future she too must fly.
William Potts becomes involved in the race to conquer the science of flight, and with his gentle daughter Polly interested only in painting, it is the hoydenish Rosie who works indefatigably alongside him in the workshop. But William will not countenance the idea of a woman flying. The ambitious and skilled Harry Clairville Jones brings further tensions to the venture. By 1906 their flying machine, Pegasus, is almost ready.
Into this smouldering situation comes a man with a hard upbringing and bitter-sad memories, who has as deep a love of the air as Rosie herself. Jake Smith's arrival sparks off a deadly rivalry. And the triumph of flight twists inexorably into tragedy and a harrowing world war.