Medical Mystery

 is a quest in Fallout: New Vegas.

Quick walkthrough
The easiest way to complete this quest is to simply wait, hidden, inside the medical tent starting at ~1:00 in the morning. Around 3:00, a private will enter, crouched, and attempt to steal the supplies. Depending on your Speech level, you have a number of options in dealing with the situation.

You can also pickpocket Private Stone and take empty Hydra (the clue) from his inventory. After that, report him to Dr. Richards.

You can also have 50 in Medicine and ask Dr. Richards about the symptoms of Hydra. After that, confront Private Stones telling him he has the symptoms.