An energy cloud-being affects the Enterprise and causes Captain Picard to leave the Enterprise.

Marc Alaimo (Antican Delegate)
John Durbin (Sestar)
Colm Meaney (Security Officer [Miles O'Brien])
Kavi Raz (Lt. Commander Singh)

• Colm Meaney's unnamed character (later named O'Brien) switches to the yellow uniform in this episode from the red uniform seen in "Encounter at Farpoint".
  
• Engineer Lt. Commander Singh is the first crew member who is killed on The Next Generation.
  
• This episode marks the beginning of Data's fascination with Sherlock Holmes.