The Doctor's rehearsal of an opera duet on the Holodeck is interrupted when he is called to treat the severely injured Lieutenant Paris, who, while aboard a shuttecraft with Torres, has been attacked by an unknown alien force. When the Doctor cannot remember the medical procedures necessary to save Paris, it's discovered that the Emergency Medical Holograph database has overloaded and The Doctor's memory circuits are rapidly degrading. While the rest of the crew fends off the cluster of alien ships — the first they've ever encountered with transporter technology in the Delta Quadrant — Torres attempts to reinitialize the Doctor's program, but forewarns that her efforts would restore the original E.M.H. program, causing the Doctor to in effect, be erased. As the rapidly failing Doctor becomes more and more disoriented, Kes pleads for an alternative remedy. So Torres leads the Doctor to the holodeck where they activate the Jupiter Station diagnostic program, a simulation of the place where his database was originally written, and find that the diagnostic matrix is a holographic recreation of his creator, Dr. Lewis Zimmerman.

Robert Picardo (Dr. Lewis Zimmerman)

• In order to save The Doctor, the Diagnostic Zimmerman Program is overlayed onto the EMH Program. The procedure saves the EMH Program, but the Zimmerman Diagnostic is no longer available.