Following a humiliating experience involving the man she thought she’d marry, Iris Tredwick signs up to the Wrens in order to escape and - hopefully - find ‘the right sort’ of man to please her mother. After a bumpy start, Iris manages to befriend outspoken Mary and dreamer Sally as they are sent to their first posting - in Orkney. There she meets engineer Rob, whose flirtatious nature both charms and confounds straight-laced Iris. Much more appropriate for her is local doctor Stewart, if only she felt the same spark for him as she does for Rob.

It is 1939, and working-class Evie Bishop has received a scholarship to study mathematics at Oxford when tragedy turns her life upside down. Evie must seek a new future for herself and, inspired to contribute to the war effort, joins the Women’s Auxiliary Air Force as an Ops Room plotter. Posted to a fighter station on the Sussex Coast, Evie befriends two other WAAFs. But the German bombers seem to know more than they should about the base’s operations, and soon Evie, May and Jess are caught up in a world more dangerous than they ever imagined.

Pearl has given up on her dreams of being a journalist after being denied a promotion because of her gender. Joining the WAAF as a radio telephone operator for Bomber Command, Pearl's new job at RAF Fenthorpe serves two purposes – providing an income for her grandmother, and keeping a close eye on her younger sister, Thea, an instrument repairer at another Lincolnshire bomber station.

Bristol, 1939. School leaver Maisie Miles suspects her father, a small-time crook, has an ulterior motive for insisting she gets a job at the W. D. & H. O. Wills tobacco factory but keeps it to herself. She's befriended by effervescent Phyllis Mason and kind-hearted Bridget Milligan who take pity on her and take Maisie under their wing. But beneath their happy-go-lucky exteriors, they all harbour dreams and worries about what the future holds.

1942. Hannah Martel has narrowly escaped Nazi Germany after her fiancé was killed in a pogrom. When her ship bound for America is turned away at port, she has nowhere to go but to her cousin Lily, who lives with her family in Brussels. Fearful for her life, Hannah is desperate to get out of occupied Europe. But with no safe way to leave, she must return to the dangerous underground work she thought she had left behind.