Oblivion's gate

Captain Benjamin Sisko takes the Defiant back in time and into a parallel universe so that he and Data can undo the vile sabotage that triggered the Temporal Apocalypse. Meanwhile, Admiral William T. Riker's grasp of reality becomes more tenuous by the minute. Can Deanna Troi free him from madness before it is too late? Starfleet's heroes risk everything to set time right. But will Captain Jean-Luc Picard let Beverley Crusher and their son die? Or will he destroy the multiverse to save them? -- adapted from back cover