In recent years, the number of studies investigating the effectiveness of using digital games for incidental second language (L2) vocabulary learning has been rapidly increasing; however, there is still a lack of research identifying the factors that affect incidental L2 vocabulary learning. Hence, the current study examined vocabulary-related (word level, exposure frequency, salience) and learner-related (language proficiency, interest, viewing captions) variables and investigated factors affecting EFL students' incidental vocabulary learning in the use of a vernacular (noneducational) murder mystery game (N = 59). The study employed a quantitative research method and descriptive and inferential statistics (repeated measures ANOVA and multiple linear regression). The results showed that playing the game greatly facilitated L2 vocabulary acquisition and retention. Among the vocabulary-related variables, the study found that only salience significantly influenced vocabulary acquisition. Regarding the learner-related variables, the students' interest and viewing captions were positively related to vocabulary learning, whereas their language proficiency levels were negatively correlated. The study found that the students' conscious attention, in conjunction with salience of the word, was the main facilitating factor in incidental vocabulary acquisition and retention in the game-enhanced language learning environment. The study suggested pedagogical implications for incidental vocabulary learning through game play based on the results of the study.