"Sub Rosa" was from the last season. I guess this episode is proof they had trouble finding good sci-fi writers by the end of the series.
Beverly Crusher, along with crew mates Deanna Troi and Captain Picard, attends the funeral of her late grandmother Nana. A mysterious man puts a flower on Nana's casket and Crusher finds it strange. Strange too that nobody else seemed to see him.
Then a groundskeeper warns her to not light this candle because it will curse the house. We later learn that's where this mysterious man's essence is kept. The essence takes the form of a man and calls himself Ronin. Ronin has made passionate love to the Howard women ("Howard" being Beverly's sir name) for centuries by turning into a green mist and enveloping them.
He does this same ploy on Beverly and it works and she resigns Starfleet to go retire in the house and bond with Ronin all the time. Picard catches her in the throws of passion when he beams down the planet's surface. He demands Ronin show himself. He does and zaps Picard and Picard is knocked unconscious and Beverley is snapped out of her trance.
The subplot has Ronin's essence creating havoc with the ship's weather regulators and causes fog on the ship and kills the grounds keeper because he knows too much. This same essence is concentrated in Nana's coffin. It's revealed through her diaries that she and Ronin were a couple for years, even when she was 93.
Beverly eliminates Ronin with a phaser blast. She rejoins Starfleet. The end.
The highlight of the episode is when Beverly is in her ship quarters and hurriedly lights the candle and waits for Ronin to appear like a junkie waiting for a fix.
This episode was a stinker. It was silly and ran more like a ghost story with simulated sex thrown in. It should have been titled 'Sub Par" or "Sub Standard."