Cathy was a young and attractive temporary receptionist hired at Dunder Mifflin while Pam Beesly was on maternity leave. During her time at the office, she developed rapport with Jim Halpert, and despite his marital status, planned to seduce him.
Little is known about Cathy's early life, although in a deleted scene, she mentions turing down a rich man who offered to marry her.
During her time at the office, Cathy maintained a fairly inconspicuous presence, and while the members of the staff who bothered to pay her any heed often maligned or trifled her (Dwight in particular), she was able to find common ground with Jim, with whom she developed a rapport. However, in "Pool Party", there are subtle implications to suggest that her feelings towards him are more than platonic. Her infatuation with him is ultimately confirmed at the end of "Special Project", when, after being selected to travel to Florida with him, and four others, for a three-week business trip, she privately informs a friend, via her cell phone, of her intentions to seduce Jim, despite his marriage and children. In a deleted scene from the same episode, she also worries about losing her job, now that Pam has returned, and implies that, in the future, she might be desperate enough to consider marrying a man she knows, named Doug, just for the financial stability he could provide.
In "After Hours", Cathy puts her plan to seduce Jim into action. She shows up at his hotel room, in rather skimpy leisure wear, claiming that the hotel maintenance crew is working in her room. While Jim initially agrees to her request to stay with him for a while, he becomes increasingly uncomfortable with her presence, especially after she uses his shower and reappears in a short robe. After she shows off her legs to him, Jim finally tells her that he is happily married, and is not interested in her. She feigns shock at this, and tells him that she had no romantic intentions whatsoever. Embarrassed for apparently having misread the situation, he apologizes, and agrees to relax. However, when he returns from the bathroom, and finds her lying under his covers with the robe on the floor, he firmly demands that she leave, despite her protests. Dwight then bursts in with chemicals to spray for bed bugs, and Jim tells him a bug is following Cathy. Dwight proceeds to chase her from the room, while Jim enjoys her distress.
In a deleted scene from the next episode, she is upset that Jim is now acting awkwardly around her, though a talking-head interview shows that she is still under the delusion that she has a chance at a romantic relationship with him. In a subsequent interview with the object of her affection, Jim tells the camera crew that he thinks she is "crazy". However, in "Last Day in Florida", it appears that she may no longer care for Jim, as she laughs along with Dwight when Dwight repeatedly insults him (although, it is also possible that she was only doing this because Dwight was Vice President to Nellie Bertram at the time). She is not shown returning from Florida with her co-workers, and in the next episode, her desk appears to be cleaned out.