“I thought you already did.”— Mark (to Serena Joy) when she refuses to betray her country.
In the TV Series
Mark meets Serena Joy in the Canadian hotel that the Waterfords are staying at during their visit. Initially, Serena assumes that he works with the press. He reveals to her that he is a representative of the US Government-In-Exile. He attempts to persuade Serena to start a new life away from Gilead, offering safe passage to Honolulu and encouraging her to write a book about the Republic that they will publish.
Realizing that he seeks to use her a propaganda tool, Mark appeals to her desire to have a baby, arguing that American scientists have been working on the fertility crisis for years and have the ability to make her fertile again. She would also be guaranteed 'freedom' (presumably not facing legal action for her involvement in the coup d'etat).
Serena states that she will never betray her country, to which Mark says that she already did (in betraying the United States of America and being part of a coup d'état which overthrew the legitimate American government).
Mark meets Serena at the Toronto airport for her meeting with Luke and Nichole. He takes her to the terminal, telling her there is a change of clothes waiting in order for her to "blend in" as the meeting is going to take place in a public area. He then introduces Serena to Luke, and is present for the whole meeting from the sidelines.
After the meeting is over, he takes Serena back to the changing room and brings up the "treason and coconuts" offer he made to her the last time they met, Serena still refuses. He leaves her alone to change back into her standard Wife outfit. It has been suggested that the phone Serena finds in her purse with a note reading "If you need me" was put there by Mark.
When Serena returns to Gilead after having seen Nichole once more, she becomes increasingly desperate to see her again. After several months of failed negotiations, in an effort to facilitate another reunion with Nichole, Serena convinces Fred to meet with Mark near the Canadian border under the pretense that he would be able to help return their daughter to Gilead.
Mark meets Serena and Fred on the Gileadean side of the border and asks them to follow his car into a safe place where they will be able to talk just "up ahead." After reaffirming that Mark is trustworthy, Serena ultimately convinces Fred to follow his vehicle, though he becomes increasingly suspicious when he realizes that the journey is much longer than expected. Unbeknownst to Fred, Mark had lured him and his wife into Canada.
Citing war crimes and documented international human rights violations, Mark carries out an arrest with the help of the Canadian military. Fred and Serena are both detained as Mark watches.
Mark comes to Serena's prison cell to prepare for her visitation with Nichole, only saying that she has been detained. When Moira arrives with the baby, he introduces Serena to her as well as a social worker, and lays down the ground rules for the visit - Moira is to stay in the waiting room while the visitation is taking place. He hears Moira's entire diatribe against what Serena and Fred have done to her and June and takes her out of the room. Later, in Fred's cell, Fred blames him for Serena's exploitation of Nichole for her own gains. Mark replies that Serena's too smart to be manipulated and tells Fred that it should be considered an opportunity to understand Gilead a little better, He also says Luke has requested a meeting, to which Fred gives his consent. Mark introduces Luke to Fred, and leaves to let the two men talk.
The next day, Mark visits Serena with a box of pizza, telling her that Toronto makes it good. When Serena implies that things like that are contraband, he simply tells her to "eat up the evidence". He also gives her a magazine and some newspapers to read, highlighting an article about media bias in relation to religion.
Mark brings Serena some coffee. Serena has been allowed to spend time outside of her cell. Mark explains that the prosecutors want to go over her written testimony and that the American intelligence debrief starts next week. Serena asks if she can decline any interviews but Mark responds that she has surrendered that right. Serena agrees to cooperate. Mark offers to push some of the sessions but she is accepts them. Mark says that she traded her rights for her daughter.
Mark tells Serena that she will have permission to leave the facility from next week as part of her reward for cooperating with the International Criminal Court. He leads her back inside and gives her pass allowing her to travel through Toronto. Serena looks forward to traveling through Toronto without an escort.
In private, Fred asks Mark if he has worked with Liz and Murray before. When he asks if he has any preferences, Fred denies this is the case. Mark thanks Fred for his patience. Fred then tells Mark that he has some information about serious crimes committed by his wife. When Mark points out that he has made an immunity agreement with Serena that she committed her crimes under duress, Fred tells Mark that what Mrs. Waterford did was beyond the laws of Gilead and the laws of God.
Serena is cuddling Nichole when she is confronted by Mark and a female officer. While the female officer takes the child away, Mark tells Serena that he has a warrant from the ICC and the United States of America for her arrest. Mark informs her that she is charged with sexual slavery and rape. Serena protests that it was a state-sanctioned ritual that was covered by the immunity agreement. Mark counters that this charge was not under duress. While a second officer cuffs Serena, Mark tells Serena that she is charged with getting her driver Nick Blaine to rape June Osborne. Serena protests that Nick's relationship with June was consensual but Mark doesn’t believe her. He tells the female officer to take her downstairs. Serena pleads with Mark but he ignores her.