While hosting a Trill initiate named Arjin, Dax discovers a tiny, developing "proto-universe," which threatens to destroy the station as it expands.

Geoffrey Blake (Arjin)
Ron Taylor (Klingon Host)
Richard Poe (Gul Evek)
Chris Nelson Norris (the Alien Man)

• O'Brien discovers that Cardassian voles — small, rodent-like creatures — have infested the station.
  
• This is the first appearance of Gul Evek.