In 2271 an unknown, cloud-like entity descends upon several Klingon vessels and destroys them. Having monitored the surprise attack, Federation space station Epsilon IX is still unable to prevent itself from becoming the next victim of this vast, mysterious energy cloud.

Meanwhile, on Vulcan, Spock is preparing to undergo the rite of Kolinahr — the achievement of total Vulcan logic — and the purging of all remaining emotion. Just then Spock's human half stirs in response to the cloud entity, interrupting his meditation and forcing the Vulcan masters to withdraw Spock's admission to their ranks.