Detective Conan S01 E438 The Fish Mail Pursuit

"One truth prevails."

The waitress of Poirot Cafe, Azusa Enomoto, reported she received strange messages from a boy, suggesting he might be kidnapped or trapped in a location without food and water. The only way to find him is by reading his text messages. The boy only knows how to send, but does not know how receive. Conan must put the clues he gives together to find out his location.