Iris is getting old. A widow, her days are spent living quietly and worrying about her granddaughter, Grace, a headstrong young doctor.
It's a small sort of life. But one day Iris receives something unexpected in the post - an invitation to a WWI reunion in France.
Determined to go, Iris is overcome by memories of the past and of her journey to France in 1914, where she followed her young brother Tom, intending to bring him home to safety. But on her way to find Tom, Iris discovers the old abbey of Royaumont, where a group of women work to set up a field hospital.
Putting her fears aside, Iris decides to stay and help.
It is at Royaumont that she truly comes of age, finding her capability and her strength, discovering her passion for medicine, making friends with the vivacious Violet and falling in love.
But war is a brutal thing, and there is a terrible price that Iris has to pay - a price that will echo down the generations.