Una, Uhura and M'Benga land on a color-drained, Klingon-occupied planet where Una is mistaken for a resistance leader who looks just like her.
Una leads M'Benga and Uhura to Mat'aar XII, a Klingon-occupied world whose sun leaves everything in black and white, to recover a probe that has drifted past the demarcation line. Stranded there, Una discovers that she is the exact double of Nevette, who collaborated with the Klingon governor while secretly aiding the local resistance, and who has just been murdered. Una assumes her identity, and Uhura survives a Klingon mind scanner by drawing on the true parts of her cover story.
As the resistance plans an electromagnetic pulse to cripple the Klingon defenses, Una frames Roman, the resistance member who killed Nevette, as the bomber, and the pulse gives the team its chance to escape. On the Enterprise, La'an's investigation into missing probe data leads to Chapel. The film noir episode features a younger Kor, the Klingon commander from the original series episode Errand of Mercy, played by Demore Barnes.