Bashir and O'Brien are hunted by the people they were helping.
Bashir and O'Brien help the T'Lani and the Kellerun, two former enemies, destroy their last stocks of a deadly biological weapon called the Harvester. When the work is done, soldiers attack the scientists, and the two escape to the planet surface, where O'Brien has been infected by the weapon.
The two governments tell Sisko that both men died in an accident, but Keiko notices the recording shows O'Brien drinking coffee in the afternoon, which he never does. Sisko and Dax find the logs were altered and rescue Bashir and O'Brien just as the ambassadors arrive to kill them to remove all knowledge of the weapon.