“Dramatis Personae” is episode eighteen of season one of Star Trek: Deep Space Nine.
A Klingon vessel returns through the wormhole from the Gamma Quadrant and almost immediately explodes. Before it does, one crew member manages to beam off it, but he dies moments after arriving on DS9.
After that, the command crew start behaving rather erratically. Kira and Sisko had had a minor disagreement about a vessel that was planning to dock – Kira didn’t want to let them, as the race in question has a history of supplying the Cardassians, but Sisko won’t do anything without proof.
The conflict gets rather more serious. The Bajorans and the Federation start splitting into two distinct sides, and people start behaving rather oddly. Sisko starts displaying a lack of interest in things, with O’Brien running things for him. Both sides start trying to recruit allies. Dax starts behaving in a rather ditsy way.
Only Odo is, of course, unaffected – although something did briefly happen to him, his personality is unchanged.