Singapore, an island country with 5.6 million population and a large volume of tourists from mainland China, was one of the first countries to report imported COVID-19 cases and had the highest number of cases outside mainland China for a time in February 2020. The government responded with a series of broadscale public health measures and managed to contain this first wave of infection. Notwithstanding that, an evolving pandemic situation in other countries eventually triggered a second, and much larger, wave of infection. This case study narrates the developments, influencing factors, and outcomes related to events starting from Singapore's first response to COVID-19 and up to the point of its entry into Circuit Breaker. It serves as a reference for the understanding and analysis of developments in an evolving pandemic and a nation's response from a systems level perspective.