Be on the case Definition 1 of 2Pro Tip 1/3Colloquial Use Used in everyday conversation, not in formal settings. The sink is leaking again? I'm on the case! Pro Tip 2/3Taking Action Implies the speaker is not just aware but actively working to solve the issue. You forgot the meeting notes? Don't worry, I'm on the case. Pro Tip 3/3Reassurance Often used to reassure someone that their concern is being addressed. Missing shipment? Relax, I'm on the case and will find it.