August 1914, London. Britain has just declared war on Germany, and the whole country seems to be in uproar. Flora, Hilda and Will, who grew up together in St Boniface orphanage, sit in the sunshine in Hyde Park on a rare day off, discussing the impending war and the changes it will bring to their lives. Will means to go off to fight, Hilda hopes to better her current lot in life as a maid at the charitable institute Hailing House, but Flora is content with her job as assistant to the Isle of Dogs' kindly Doctor Tapper. Taking a vow, they pledge to always be there for each other, come what may.

It soon becomes clear that the war will not be over by Christmas, as so many thought, and the first zeppelin raids bring casualties flooding into the surgery where Flora works. Tragedy strikes in the trenches, too, and Will returns home with physical and mental wounds too deep for Flora to nurse back to health.

In the meantime, Hilda has taken herself away from London to work as a maid at the sumptuous house of Adelphi. But it is not long before she finds herself out of her depth. And the consequences of her choices will lead to a shocking discovery that will change the course of the three orphans' lives forever.