Lady Irena is the owner of "Lady Irina's House" where the murder victim Jessica Margolis worked. Jessica's roommate Danielle tells Castle and Beckett that on the evening of Jessica's death, strangely, a wine glass with a red lipstick mark was left on the table. Castle recognizes the color again immediately as the shade worn by Lady Irina. When they ask Irina, she basically takes the Fifth. In the end it turns out that she had been so uncooperative because, well, she's a lawyer and a dominatrix.