The Doctor falls in love with a Vidiian patient.
The Doctor treats a Vidiian woman who is dying of the phage and, because her body cannot survive, transfers her consciousness into a holographic form. The two develop a bond that causes the Doctor to question the nature of his own existence.
The episode gives the Doctor one of his earliest romantic stories and offers a kinder portrait of the Vidiians, a species that had been seen mainly as a threat. It also shows how far the character has come since the pilot, and how his ability to care for people is a result of his programming and his own choices.