"Who's the Thief?" is a dynamic ESL activity designed to develop students' reading comprehension, vocabulary, and critical thinking. Participants take on the role of detectives tasked with solving various cases. Each case presents detailed physical descriptions and personality traits of suspects, such as hair color, clothing, and distinguishing features. The goal is to examine clues and identify the guilty individual from a set of suspects. This interactive resource encourages collaboration and careful observation, making it perfect for group work in intermediate-level ESL classrooms.