She manipulates Scott Tyler in order to make her plan work to successfully control an armed guard's mind and make him shoot Senator John Trelawney and make Senator Charles Baker become president of the United States, who supports the Old One's return. She takes Scott to a juvenile prison centre called Silent Creek.
Mortlake is the woman who organized the attempt to kidnap Jamie and Scott, which half-failed, so she ordered one of their attackers, Colton Banes, to strangle his partner Kyle Hovey. Mortlake works in Los Angeles and she is one of the chief executives of Nightrise, probably under the chairman, whom she takes orders from. The chairman briefly considers her resignation after her plan fails, but the chairman lets her stay on the board.
Mortlake arranges for John Trelawney to be shot, which is why she wants to twist Scott's mind: to make him able to shoot Trelawney by telepathically communicating with one of Trelawney's men. Susan Mortlake almost succeeds in accomplishing this plan, by blocking Scott's mind from other people's minds, so when Jamie tries to contact his brother's mind, he is blocked out. However, Jamie contacts Trelawney's henchman, and, at the last moment, directs him to shoot Susan Mortlake instead. This act is described as 'the most terrible order' of Jamie's life.
Susan Mortlake is obviously the counterpart to Susan Ashwood, one of the members of the Nexus, although Mortlake has also probably been given power by the Old Ones, as she looks deathly pale.
She is pale for a human and she also has a long neck, similar to Salamanda, and very short gray hair. She is supposed to look quite masculine.
Susan has a son called Jonas Mortlake, who is an antagonist in Oblivion, he follows in his mother's footsteps by bullying and twisting Scott's mind. It is mentioned that he never saw his mother much, although he didn't mind as he didn't particularly mind her. When she died, Jonas did not go to her funeral but instead continued working for Nightrise, but he did vow to avenge her.