The Ponyville hospital is in crisis. The psych ward is overflowing with ponies displaying the symptoms of a peculiar new disease, and Dr. Stable is baffled by their resistance to all but the most extreme of treatments.

Meanwhile, nurse Gentle Mint does her best to treat the infected ponies, but her secret changeling nature poses a risk to the entire hospital. She is trapped- reveal too much, and she will be sent to the Canterlot dungeons for interrogation, but reveal too little, and the ponies under her care will begin to die.