Star Trek: Deep Space Nine (sometimes abbreviated to DS9) is a science fiction television series set in the Star Trek universe in the Milky Way galaxy, in the years 2369–2375. In the beginning of seeson 5, Starfleet assigns Sisko to expose the Changeling infiltrator in the Klingon Empire. And while exploring in the Gamma Quadrant, Sisko, Dax, Worf, and O’Brien see a Jem’Hadar warship crash on a planet’s surface.