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 season 4, A Klingon fleet arrives on its way to expand the Klingon Empire at the expense of the Cardassians in the face of the Dominion threat, and Worf is brought to DS9 to negotiate.