Teacher continuing professional development (CPD) is almost always on the top of educational agendas in any country of the world. While existing studies primarily emphasize effective CPD programmes, this qualitative research seeks to deepen our understanding by examining the nuanced interplay of teacher's unique working contexts, historical backgrounds, and social influences within the CPD landscape. To investigate the strong shocks resulted from the special period of time - the COVID-19 pandemic - to teachers and the approaches to accommodate the issues on the basis of the workplace, this qualitative study adopts a longitudinal, single case design to examine a Chinese language teacher's boundary crossing in CPD during the period of the COVID-19 pandemic. Data was collected over a period of seven months, from the beginning of January 2023, the time of the COVID-19 pandemic to the end of July 2023, students returning to school. Guided by boundary crossing and Cultural Historical Activity Theory (CHAT) theoretical frameworks, this study suggests that the teacher employed a variety of CPD tools which supplemented and interconnected for different CPD objectives. CHAT conceptualize the complexity and the dynamic nature of CPD and contextulize the trajectory of boundary crossing. By employing a nuanced and comprehensive approach, this study contributes to the ongoing discourse on teacher CPD, recognizing the complexities of teacher CPD and the intricate interplay of contextual factors that shape teachers' professional development trajectories.