The Doctor's program is sent back to the alpha quadrant via subspace to help treat his terminally ill creator Dr Zimmerman.
What follows is a battle of wills between an obsessive Doctor and a difficult patient who does not want to be treated by him. The plot concludes in a clever way, whilst giving us a plausible reason for Zimmerman's behaviour, not just making him difficult for the sake of a story.
The plot has been criticised for not taking simpler options than The Doctor take on such a high-risk mission when other options are clearly available. Well, the key to appreciate this episode is to just enjoy the confrontation between two characters and accept they have to share the screen for the full affect. When you get past the plot-hole, sit back and absorb what comes next.
Robert Picardo is on scintillating form playing both creator and creation. He delivers a masterclass in physical and emotional performance that keeps you engrossed in both characters. It's comparable to the bickering interaction between the two distinct characters such as Frasier and Niles Crane or Oscar Maddison and Felix Unger, just performed by a single actor.
There is able support from the Reg Barclay and Deanna Troi characters, but the two Docs blow everyone else off the screen.