The Visitor

On a stormy night far in the future, a young writer named Melanie calls on the elderly Jake Sisko, a celebrated author who stopped writing long ago, and he tells her why. Years earlier, as the Defiant observed a rare inversion of the wormhole, an accident in the engine room struck Captain Sisko and he vanished in front of his teenage son. Benjamin had not died. He was trapped in subspace, snapping back into Jake's life for a few moments every few years. Jake gives up his writing and his marriage to study subspace mechanics, obsessed with bringing his father home, while Benjamin begs him to live his own life. Realising that the two of them are linked, the dying Jake arranges to be with his father at the moment of his own death. The link is broken, and Benjamin is thrown back to the instant of the accident, in time to save his son's younger self.