The Idiom Mystery is an international eTwinning project for young learners (elementary school students in grades 1-3) to explore the fascinating world of English idioms. Working together with classmates from different countries, students will create a digital dictionary of English idioms creating visual representations, such as "a bird in the hand is worth two in the bush" or "to be a piece of cake" and a series of videos showcasing the meaning of idioms. Teachers will collaborate to develop interactive activities such as crossword puzzles, memory games, and bingo, to enhance students' understanding and engagement with the idioms as well as online quizzes and games to test students' idiomatic knowledge.