May, 1915. Alfie and his fisherman father find a girl on an uninhabited island in the Scillies - injured, thirsty, lost... and with absolutely no memory of who she is, or how she came to be there. She can say only one word: Lucy. Where has she come from? Is she a mermaid, the victim of a German U-boat, or even - as some islanders suggest - a German spy...? Only one thing is for sure: she loves music and moonlight, and it is when she listens to the gramophone that the glimmers of the girl she once was begin to appear. WW1 is raging, suspicion and fear are growing, and Alfie and Lucy are ever more under threat. But as we begin to see the story of Merry, a girl boarding a great ship for a perilous journey across the ocean, another melody enters the great symphony - and the music begins to resolve...