Tahna Los, a former Bajoran terrorist during the Occupation, asks Sisko for asylum on DS9. Meanwhile, the station's last Cardassian inhabitant, Garak, possibly a former spy for the Cardassian government, proves an interesting mystery to Dr. Bashir.
Ibudan, a criminal Odo has dealt with before, returns to DS9 only to be murdered shortly after - leaving Odo to be the prime suspect. Jake and Nog's trouble making prompt Keiko to do something helpful for the station's children.
The crew and civilian population of Deep Space Nine begin to speak gibberish when a plague - an 'aphasia virus' - engineered by the Bajorans as a weapon against the Cardassians, accidentally gets released into the station's atmosphere.
Out of nowhere the entire station's command staff, save Odo, become power hungry and vie to defeat each other by forming secret alliances and plotting assassinations. Needless to say, Odo tries to figure out how this mysterious behavior was influenced.