While conducting routine operations near the former Federation–Cardassian border, the USS Ermiana intercepts a faint, severely degraded Starfleet distress transmission.

The signal originates from the USS Halcyon, a Miranda-class starship that disappeared six years earlier during the Federation–Cardassian Border Wars while undertaking a classified assignment. Presumed destroyed with all hands, the Halcyon has remained missing ever since.

Captain Mikoto Misaka orders the Ermiana to investigate the mysterious transmission. However, upon locating the missing vessel, the crew discovers that the ageing starship has suffered extensive damage and has been drifting through space for years. As the Ermiana attempts to establish contact and uncover the circumstances surrounding the Halcyon's disappearance, it soon becomes clear that the original Starfleet reports may not tell the whole story.

What really happened to the Halcyon six years ago, and why has its distress call only now been detected?