Munitions worker Rosalind Graham longs to choose her own life and escape her guardian's manipulations. On Rose's last day at the Chilwell factory, co-worker Tilly Lockhart plans a farewell party and the two exchange IDs so Rose can await Tilly at her flat. But the factory explodes, killing hundreds, including Tilly. Realizing the world thinks she is dead, Rose sees her chance to escape. She assumes Tilly's identity and takes a supervisory job in Gretna, Scotland.

RAF Captain Alex Baird returns home on a secret mission to find the saboteur suspected in the Chilwell explosion, knowing Gretna's factory is next. He's surprised to discover Miss Lockhart renting his boyhood room, but the two eventually bond over their mutual affection for his family--until Alex receives orders to surveil her.

Rose squirms beneath his scrutiny while struggling to gain her workers' respect. But the danger of her deception intensifies when a mysterious package addressed to Tilly arrives. Will Rose's daring bid for freedom be her greatest undoing?