After a climactic battle over the Klingon homeworld, Toral is defeated. He retreats to the Neutral Zone, revealing that he was getting assistance from the Romulan Star Empire. Hostilities ensue between the Klingons and the Romulans.
The Romulans, in the meantime, come across a stable Omega Particle, a source of nearly limitless power. The particle, discovered first by a Ferengi mining guild, is about to be sold to the Cardassians; the Tal Shiar sends Admiral Sela to secure it before that happens. Sela captures the Omega Particle and, despite some Borg interference, delivers it to a fortified Romulan base. She then allies with the Borg promising the particle after they destroy Toral's remaining forces, but she then betrays and attacks them after Toral is defeated.