Passenger

Milan and Roma are twins. They've lived together for years but only just met
Milan, a violinist in a London orchestra, becomes aware of strange musical clicking sounds seeming to come from inside himself. A series of medical tests gradually reveal that before his birth he somehow managed to subsume his twin sister - an occurrence termed medically 'foetus in fetu'.
Milan names his sister Roma and embarks on the task of trying to introduce her to the world outside. He enlists the help of young special needs teacher Murri and together the three of them conduct a series of experiments to enable Roma to express herself...Like the pigeon in Patrick Suskind's book of the same name, the discovery of Roma causes a revolution in his life.