It's the night before Rose's mum re-marries. Rose can't sleep for worrying and nor can her muddled Great-Aunt Cosy, her namesake. Rose sees the old lady leaving the house and runs after her to the London underground. Their empty train stops in 1940, in a war-torn London broken by the Blitz. Here, Rose witnesses great romance and impending sacrifice. Tragedy will surely follow - unless she can change what happens next ...