Whilst working in remote South America, Robin Stanton hears that his beloved sister, Carol, has committed suicide. He refuses to believe this and returns to England. He starts to probe into Carol's death, becoming more and more convinced that she was murdered. He finds her diaries, which lead him to think that she was being set up by British Intelligence - or someone more sinister. Meanwhile, he falls in love with Jackie Fremington - but is she more involved than she admits?