New York attorney William Singer received some personal items from the estate of his recently deceased sister. There he also found three letters that initially made him doubt the sanity of his German relatives Josefine Eylandt, describing how she and her family had hidden people in her cellar for decades. However, the first research quickly gives rise to the suspicion that there is a real story hidden behind the letters. Singer hires a German private investigator. Together they collect evidence that suggests that the Eylandt family has hosted three guests from another world for many decades.