Wit Sec receives a homeless but genius man who witnessed a homegrown bomb attempt & called the authorities, saving hundreds of innocent people. Walter Cooper (Esteban Powell) once lived off the streets of Seattle Washington & consumed the many books at the library he lived in. But now, Mary & Marshall have to clean up this federal witness to that he’s a credible witness for the U.S. Attorney’s case. After cleaning up, Walter starts a job at a local Albuquerque bookstore where he’s anything but receptive to the idea of an alarm clock, schedule, uniform & nametag. When Wit Sec uses a federal databank to track down a wanted local fugitive on the FBI’s top ten list, Walter gets the idea to use the same method to find his birth mother. Adopted at a young age, Marshall & Mary find out where Walter’s mother is located but must race against time to reconnect the two after they find out that she’s in grave trouble. ...

A teenager witnesses a bloody diamond store heist & she is immediately introduced into Wit Sec protection. However, her mother stays behind & lets her father accompany her. Mary takes the reigns & finds that Sabrina (Spencer Locke), the daughter, is torn between her separated parents who dislike one another. Her mother (Jessica Tuck) barely has any time to see her on planned visitations in Chicago, & her father (Christopher Cousins) thinks he can buy her love with cars & gifts. Mary is left to emotionally guide her as the "stepmother" & make sure that Sabrina makes her federal hearing to testify against the criminals. Meanwhile, Scott’s gambling debts have caught up with him. He ends up in the hospital, badly beaten. He claims that he was mugged & robbed, but Brandi is beginning to think there are other factors at play. ...

Gabriel Adams (Joe Spano) witnesses a stripper’s death when an argument between two sex traffickers spills out into the main club lounge. After his relocation to New Mexico, Gabe eagerly accepts his new role as a bartender. But the more that Mary checks on the priest leading up to his federal case, the more she finds out about his immoral past. Meanwhile, Stan must confront the daughter of a witness, Roy Keels, who has died under protection. She comes to find out more about her father & after lying to her about his character, she finds out that he was nothing but a "petty" criminal. Mary’s personal life is shaken up when Brandi & Peter announce that they’re moving in together. & Marshall & Jinx pressure her to use her vacation days before they expire under new Wit Sec rules. ...

Mary & Marshall's first case together in 2003 is revisited after an amorous couple in Baltimore witnesses the brutal killings of the boyfriend's family. Marshall & a reluctant Mary must transport Henry Doer (Josh Cooke) & Claudia Tobin (Jeannine Kaspar) across the country to the safe haven of Albuquerque. Flash-forward to 2010: Mary & Marshall are rehashing this first case when the couple
- now on the road to romantic ruin
- jeopardises their identities when Henry comes to realise that the romance has died. There's also a new face at Wit Sec headquarters. The newly appointed U.S. Marshall in town Allison Pearson (Allison Janney), doesn't make a very good first impression with Mary. Mary's sister, Brandi (Nichole Hiltz), is struggling to have her tuition check refunded. & Peter even offers to help her financially, but Brandi has plans of her own.

...

An ATF agent is gunned down when an arms deal goes bad in El Paso, Texas. After awaking from a coma three years later, Wade Guthrie (Mike Doyle) is placed under Wit Sec protection as a star witness in a federal case. Wade's longing to be reunited with his past girlfriend leads Wit Sec into a dilemma as his partner & former girlfriend are now much more "acquainted." When Wade breaks free of US Marshal custody in order to see his former girlfriend, Mary & Marshall go into damage control mode & try to pacify an explosive situation. Also, Marshall relies on fate to link himself with a beautiful pharmaceutical saleswoman named Breck. Could this be love or just a flash in the pants? Meanwhile, Mary juggles the arrival of her fiancée's aunt, who is representing Raph's mother at the engagement party, & the new head at Wit Sec, Allison Person, who is making life difficult for Mary. ...

Mary & Marshall travel to Providence, RI to observer their witness' trial when Dominic Difazzio (Louis Lombardi) becomes a star witness against his uncle & mob boss, Vincent Difazzio (Roy Costley). Given Difazzio's murderous track record with explosives, he's not one of Mary's favourites. After settling into his new life in New Mexico, Difazzio opens a local fish store & falls in love with a business neighbour named Naomi (Salli Saffioti). The only problem is that he doesn't know how to act around women, having never been on a date. He begs Mary for a little advice, & she grudgingly agrees. Mary says her goodbyes to Raphael (Cristián de la Fuente), only to run into him later when she accompanies Difazzio on his first date. Difazzio's date goes swimmingly & he tells Mary that he thinks he sees wedding bells in his future. ...

Thirty-eight years ago, Frank Jergens' (Fred Ward) good side showed itself while he was robbing a bank. During the heist, he turned on the dirty cops who were helping him pull it off. After 38 years in the pen, Jergens is released to Mary & Wit Sec, but not before making friends & connections on the inside. Mary is very concerned about Frank's friend, Ray (Brian Goodman), who is indebted to two criminals who are eager to collect. & the more that Mary engages with Frank, the more she is reminded of her father. When Frank's friend Ray shows up at his door in dire straits, Frank must decide whether life on the outside is as good as it's cracked up to be. Meanwhile, Mary gets into trouble with Wit Sec administrators when they find out she's been abusing U.S. Marshal services to track down her sister. Marshall also has his hands full with an ex-writer who is falling apart with her life under protection. ...

Marshall packs his bags for a witness escort out of state, leaving Mary behind in Albuquerque with FBI agent Mike Faber (Steven Weber), who's in town with a federal witness in need of protection from the Russian mob. Natalie Vickers (Alexandra Lydon) was once a part of a mortgage scam in Los Angeles, but now she's under Mary & Faber's watch. Seemingly too nonchalant about entering Wit Sec, Natalie has apparently attracted her accomplice & boyfriend to Albuquerque where they continue to operate real estate fraud & get caught in the process. The sexual tension between Mary & Faber rises, as the two of them work closely to stop Natalie from indulging in her criminal past. When Mary realises that Natalie is doing it all for love, the boyfriend becomes a target of the FBI. Yet, Faber has another conflict to deal with, his superior officer in charge Ike Dennis. After being promoted, Ike doesn't gel any more with the lower ranks. ...

Marshall's newest witness Billy was once a drug runner who witnessed a drug-deal gone deadly. Now taken under Marshall's wing, Billy is admitted into Albuquerque's best boarding school & urged to find friends who will accent his personality. If this wasn't enough of a load, Marshall's father, Seth shows up in Albuquerque on a sting operation called Operation Falcon that targets open warrants in the area. Marshall's straight-laced style contrasts with his father's maverick approach when he & Mary join Seth on his assignment. All hell breaks loose when Marshall finds out Billy is involved in one of Seth's open-warrant apprehensions of a local criminal named Liam. Marshall seemingly works against his father in clearing Billy of any wrongdoing after finding out his witness' ulterior motive & relation to the crime. ...

Mia Cusato’s (Laura San Giacomo) life turns upside down after she shoots & kills her own uncle (Michael Badalucco) who was attempting to "whack" her. But Cusato’s future in Wit Sec is imperiled after she reveals a condition she’s hidden from her family, a condition that may make her a questionable federal witness against her mob boss husb&. Cusato & Mary hit it off when Mary discovers that their lives aren’t so different from one another. Mary pulls all the stops to make sure that Cusato will remain protected while being interviewed by the attorney general in charge of the case. Marshall also has his hands full with a witness, Patrick (Travis Schuldt), who has been secretly been involved with his gay lover, Bob (Evan Gamble). Bob had relocated to Albuquerque after Patrick entered Wit Sec. Marshall must figure out a way to talk Bob into entering Wit Sec so that the two can live together. Jinx comes close to relapsing after Brandi reveals that she has a half-brother ...