The phrase "on the case" is commonly used to describe someone who is actively investigating or pursuing a matter. Synonyms for this phrase include "working on it," "looking into it," "handling it," "taking care of it," "dealing with it," and "managing it." These synonyms all convey a sense of diligence and determination, as well as a commitment to resolving the issue at hand. Additionally, they can be used in a variety of contexts, from professional settings to everyday conversations. Whether you're a detective solving a crime or a parent addressing a household issue, using synonyms for "on the case" can help you convey your intent clearly and effectively.