be on the case

1. To be working diligently on a particular task. Yes, there is a problem with my car, and my mechanic is on the case. Our team of engineers is on the case to fix the issue, and we thank you for your continued patience with the matter. I know you weren't expecting company tomorrow, but don't worry—I called the housekeeper, and she's already on the case.

2. To be investigating something. When my youngest thinks her older brother is doing something suspicious, she is on the case—she's the best spy I could have asked for! The system crashed overnight, but IT is on the case, so it should be back up soon. Sir, we will recover your stolen goods—our top detective is on the case.

be on the case

If you are on the case, you are dealing with a particular problem or situation. Note: In the first two expressions, a case is a matter that is being dealt with by a lawyer or doctor, rather than referring to a box or suitcase. I need to organize the party, I know — I'm on the case. Often these missions are just a chance for politicians to show the folks at home they're on the case.

be on the ˈcase

be dealing with a particular matter, especially a criminal investigation: We have two of our best agents on the case.