Tiffany Harper is Lucas' ex-girlfriend, who shows up the day after the killing in the restaurant. It is suggested by some of Tiffany's comments that she broke up with him due to his intimacy issues. He still has feelings for her and it is possible to rekindle their relationship in the course of the game. She is kidnapped by the Oracle and used as bait. When Lucas comes to save her, the Oracle collapses the wooden roller coaster where he was holding her prisoner and she dies from the fall
Source: Wikipedia, "[en.wikipedia.org/wiki/Fahrenheit_%282005_video_game%29%23Plot Fahrenheit (2005 video game)]", available under the CC-BY-SA License.