Wallace Ryman has devised a system that comprehends all of this – but he is a reclusive pacifist who stubbornly refuses to divulge his secrets. Mark Latchford, a young maths prodigy from the Met Office, is sent to Scotland to discover Ryman’s system and apply it to the Normandy landings. But turbulence proves more elusive than anyone could have imagined and events, like the weather, begin to spiral out of control.