A star system suffering an outbreak of an unclassified strain of plasma plague in 2365, which sent the Enterprise to collect dangerous specimens for research into a cure.
The Rachelis system drives the secondary plot of the Next Generation episode The Child. With the epidemic there spreading, the Enterprise is sent to Aucdet IX to take aboard samples of plasma plague and carry them to Science Station Tango Sierra, where a countermeasure may be developed.
The medical trustee Hester Dealt supervises the loading of the specimens into a containment module built to Geordi La Forge's design. Any leak could kill everyone aboard within hours.
During the trip one strain begins to grow inside its sealed container. The cause proves to be a rare radiation given off by Ian Andrew Troi, the rapidly ageing child born to Deanna Troi, and the being ends its visit and returns to its natural form so that the ship will be safe.