Located in an area of non-aligned space near Federation and Romulan territory, the Kondaii system is home to a unique stellar phenomenon: a spatial rift that opens every three years in proximity to the system's sole inhabited planet. Only during this brief period is communication possible with the small, mineral-rich planetoid inside the rift. The local population has established a mining colony on this planetoid, and for the limited duration that the rift is open, a massive interplanetary operation is set into motion: ferrying mineral ore to the home planet while simultaneously transferring personnel and replenishing essential supplies and equipment—everything necessary to sustain the colony before it once again enters forced isolation.
While studying the rift, the science vessel USS Huang Zhong is severely damaged and crash-lands on the planetoid. After the starship Enterprise arrives to conduct rescue operations, evidence quickly points to the rift's artificial nature. It is a feat far beyond the capacity of the local inhabitants, and presents an alluring mystery for Captain James T. Kirk and his crew. It also attracts the attention of the Romulans, who are most interested in studying and perhaps seizing this supposed advanced technology—by any means necessary.