Four-and-a-Half Vulcans

Pike, Chapel, Uhura, and La'An are transformed into Vulcans for a mission, after which they decide to remain Vulcan. Pike becomes obsessed with efficiency and neatness; Uhura manipulates Beto into accepting a mind meld to improve their compatibility for a potential relationship; Chapel ends all of her friendships and her relationship with Korby to focus on work; and La'An develops Romulan tendencies, becoming a sinister warmonger. At a meeting regarding Batel's request to return from medical leave to her job with the Starfleet Judicial Department, Pike tells Vice Admiral Pasalk that her return would be illogical, and Batel loses her temper with both. Scotty and James Kirk, on leave from the Farragut, become friends while working together to stop La'An.

Summary from Wikipedia, CC BY-SA 4.0.