The setting is on a remote station or outpost on a planet I believe. The character whom the narration follows (1st or 3rd POV) has only objects like a telescope and a radio transceiver to communicate.
The exact means the plot precipitates is not important, but I believe a coordinated war breaks out or surprise ambush on earth related systems takes place. The relativistic passenger liner takes defensive measures, which I believe the narrator/main person observes. The ship extends thousands-of-kilometers-long cables, which at relativistic speed will collide with matter in the system to effectively sterilize it.
The author or main voice has to convince the captain that he is not hostile and that the captain should allow his system, which may be synonymous with himself, to survive the ship's passage.
The radio delay and the decreasing window of time create the suspense. The message is a telegram basically, and the window of resolution is decreasing by the ship approaching at high relativistic speed.
This concept was unique in the stories I have read, to my knowledge. I'm actually trying to count the general case for how many messages can be sent back and forth until the reaction time is on the order of travel time.