This paper examines the impact of the COVID-19 pandemic, and the resulting investor-sentiment in determining portfolio returns of healthcare, telecommunication, insurance, banking and hotel sector companies in the Colombo Stock Exchange, Sri Lanka. A first-stage event study methodology and a second-stage regression-based methodology are adopted to evaluate the impact of pandemic-related-news to identify the influence of investor-sentiment on sector portfolio returns and its persisting effects. The most striking phenomenon is positive and persisting Cumulative Average Abnormal Returns perceived after a long Island-wide lockdown curfew is lifted on 11-May-2020. Results of a second-stage regression-based analysis indicate an initial negative sentiment, followed by a positive sentiment thereafter. The initial negative effect is relatively robust on banks and hotel sector stocks. A positive sentiment emanates from over-reaction to the subsequent rebound. CSE-investors are more sensitive to local events than to global news, and are likely to react based on psychological biases, signifying irrational investor behaviour.