Susan Langdon worked as a FBI agent and was assigned to the case of the Welfare Mom Serial Killer who had killed up to 8 women. Angry over being taunted by the killer, Susan falsified evidence after a ninth victim was found dead, resulting in the killer getting prosecuted. Susan wrote a succesful book about how she captured him and then became a forensic pathologist.
Susan appeared at Quantico to give a class on serial killer cases, assigning the task to find the one murder that doesn't fit their profile. She is encounted by Simon Asher, who asked Susan about the Welfare Mom Killer's ninth victim, noticing that the murder doesn't match his profile. Susan brushes it off, but Simon continued to bring up the subject while she and the NATs were at a bar relaxing.
Simon figured out that Susan planted the evidence on the scene of the ninth victim, doing so to finally arrest him. At that moment, the evil Susan admitted to the ruse and threatened to kill Simon to keep her secret hidden. She planned to kill him with a pulmonary embolism and later took him outside so she could commit her murderous act, all while threatening Simon with a syringe. At that moment, Ryan Booth caught Susan and Simon and wondered if anything was wrong, derailing Susan's plan to kill Simon. She later kisses Simon while telling him that he can't prove a thing. Susan's ruse was leaked by Simon later on, forcing the FBI to release the killer. Susan was arrested (off-screen) for her crimes, which included her attempt to kill Simon.
A charming teacher and famed investigator Susan Langdon has a dark side to her personality. After framing a suspect with false evidence she was willing to threaten and possibly even kill Simon to cover it up.
A cunning tactician Susan was able to isolate Simon in a crowded bar and take him hostage while pretending they were going home. Setting him up for a perfect murder as she would kill him without leaving evidence. However her scheme failed as NAT Ryan noticed the stiff manner in which Simon was herded away.
- Anne Heche also portrayed femme fatale Tanya Sullivan in the film Fatal Desire as well as Jeniffer, the main antagonist and murderer in the 1994 TV movie Girls in Prison.