Young-Hee Seong is a Korean immigrant and Mary Kay beauty consultant who Elizabeth Jennings befriends in her "Patty" disguise as a means of gaining access to her husband Don who can provide the 'Level 4' security code that William needs to obtain deadly specimens.

They become good friends before "Patty" drugs and manipulates Don into thinking he has slept with her, and later, that she has become pregnant. Don tells "Patty" to get an abortion. Later, disguised as her family, "John", Gabriel and another agent visit Don at work announcing Patty has killed herself, and demanding money to pay for funeral expenses. When Don leaves with Philip to retrieve the money, Gabriel and the agent posing as his wife copy his computer discs and gain the access code to level 4.

Don's guilt over his supposed role in Patty's (fake) pregnancy and death causes irreparable strain between him and his wife, causing Young-Hee to grow increasingly frantic in her attempts to contact Patty. Elizabeth agonizes over her destruction of the Seong family, and the loss of their friendship. She later parks outside their house and is surprised to see they no longer live there, indicating their marriage did not withstand her actions.