When Troi's shuttle crashes on the planet Vagra II, a sadistic alien named Armus with great power blocks her rescue, kills Lt. Yar and threatens to kill Riker and Troi.

Mart McChesney (Armus)

Ron Gans (Voice of Armus)
Walker Boone (Lt. Cmdr. Leland T. Lynch)
Brad Zerbst (Nurse)
Raymond Forchion (Lt. Ben Prieto)

• Lt. Worf is made acting Chief of Security.
  
• Denise Crosby left the series because she was unhappy with her character and she wanted to pursue a movie career. She will return as Romulan Commander Sela and guest stars as Lt. Yar in "Yesterday's Enterprise" and "All Good Things..."
  
• This episode was produced before "Symbiosis" but was aired after "Symbiosis" so the production numbers are out of order.