It is 1942, and the war is not going well. As part of the war effort the Ashworth Grammar School for Girls signs up for the Merchant Navy's Ship Adoption Scheme, as the headmistress believes the project will broaden her girls' horizons. Aboard their adopted ship, the SS Treverran, Captain Josh Percival is tasked with beating the U-boat blockade. His wife Jessica is a Wren officer at Liverpool's Derby House, and son Peter in the Royal Navy. All is as it should be until Captain Percival and his officers visit Ashworth School. The choices that follow will disrupt all their lives, reverberating even to the next generation.