Dr. Crusher jeopardizes her career when she delves too deep into the murder of Dr. Reyga, a Ferengi scientist whose interphasic shield invention may have been coveted by others.

Whoopi Goldberg (Guinan)
Patti Yasutake (Nurse Alyssa Ogawa)
Tricia O'Neil (Kurak)
Peter Slutsker (Dr. Reyga)
James Horan (Dr. Jo'Bril)
Joan Stuart Morris (Dr. T'Pan)
John S. Ragin (Dr. Christopher)

• The interphasic shield allows a ship to fly into a star's corona, protecting it from heat and radiation.
  
• Kurak is a Klingon warp specialist. Both she and Dr. Reyga experience prejudice because their chosen professions are outside of their culture's norms.
  
• Dr. Jo'Bril was a Takaran scientist. Takarans can control their bodies at a cellular level, and can appear to be dead.
  
• Dr. Crusher will use Dr. Reyga's interphasic shield in "Descent, Part II", defending the Enterprise from the Borg. The interphasic shield will later become standard equipment in new Federation starships, such as the Intrepid-class U.S.S. Voyager.
  
• This is Guinan's last appearance on The Next Generation. She will later appear in the motion pictures Star Trek: Generations and Star Trek: Nemesis.