Barclay's fear of being transported intensifies after he encounters mysterious creatures while transporting back to the Enterprise from the U.S.S. Yosemite, a marooned ship.

Dwight Schultz (Lt. Reginald Barclay)
Colm Meaney (Chief Miles O'Brien)
Patti Yasutake (Nurse Alyssa Ogawa)
Renata Scott (Admiral Hayes)
Thomas Belgrey (Crew Member)

• O'Brien, who was a full Lieutenant up until this point, loses his two solid pips which are replaced by one hollow pip. According to the producers, O'Brien was always supposed to be a non-commisioned Chief Petty Officer and this episode corrects his (six-year) "wardrobe mistake." The change was made for Colm Meaney and O'Brien's pending move to the new series Deep Space Nine.
  
• Barclay was introduced in Season 3's "Hollow Pursuits".
  
• The U.S.S. Yosemite NCC-19002 is an Oberth-class science vessel.
  
• Troi teaches Barclay a Betazoid relaxation technique called "plexing" (stimulating a pressure point under the ear). Troi is seen doing this in later episodes, like "Timescape".
  
• This is the first episode to show a transporter cycle from a first-person point of view.
  
• Barclay fears that he has "transporter psychosis", first diagnosed in 2209. There is no cure.