Jessica Fletcher is on a train headed for El Paso. She shares a table in the dining car with a woman who subsequently vanishes, leaving her purse on the table. Then a message is announced for the woman and Jessica accepts it. This leads to an attack in her compartment and a demand for 'it'. She has no idea what 'it' is and is rescued by a man claiming to be a journalist. The plot thickens. She is warned away by an FBI man, but continues to follow her clues to Agua Verde where the woman apparently lives. The plot twists and turns as she delves deeper in a most devious mystery.