TV Guide reports:
Acker will play an attractive psychologist who caters to the rich and powerful. When the machine spits out her number, Reese (Jim Caviezel) must keep her safe from several clients who could potentially kill to keep their secrets safe.
Acker is best known for her work on Angel and Alias, as well as more recent appearances on Grimm and Once Upon a Time.
Person of Interest's Season 1 finale airs May 17 at 9 pm on CBS.