Complex sentence: It takes place in the later years of the timeframe, focusing not on the crew of the "USS Enterprise", but on a different Constitution class starship, the "USS Exeter", NCC-1706.
Split into simpler sentences: It takes place in the later years of the timeframe. It focuses not on the crew of the "USS Enterprise", but on a different Constitution class starship, the "USS Exeter", NCC-1706.