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 ...

Pregnant or not, Mary Shannon has never been very good at unwinding. Which is why, in an attempt to force relaxation on her, Stan & Marshall hatch a plan to get her out of town. With Oscar riding shotgun, Mary heads into the desert to deliver a message to one of Marshall's witnesses, a new age alpaca farmer who just might have some insight to offer into Mary's current situation. & with a file full of prospective adoptive parents & some tough decisions to make, Mary could certainly use a little guidance, even if she is reluctant to heed the advice of a New Mexico mystic. Or a dog. ...

When a decorated soldier witnesses his superiors selling arms to the enemy & steps forward to do the right thing, he soon finds himself out of the Army, shipped off to Albuquerque, & in the Witness Protection Programme. Like most witnesses, John & his wife Sue have some trouble coping with the changes, but unfortunately their problems run deeper than adjusting to life off the base: John is suffering from Post Traumatic Stress Disorder, & his psychological state is putting the case & the witnesses in jeopardy. ...

Mary proves it takes one to know one when she visits a mafia-mistress-turned-witness named Grace Haddik, & discovers what both Marshall & Stan missed: Grace is pregnant. Very pregnant. Now that Grace's bun in the oven is out in the open, Mary & Marshall must do their best to keep mother & baby safe. Which in Mary's case means posing as Grace's life partner & holding her hand through the birthing process. ...

Brandi's wedding day has finally arrived, & Mary finds herself torn between two duties: job & family. The one day of the year she can't be at work, Maid of Honour Mary is called in to testify about her role in the sting on arms dealer Julian Conran, & she can only hope to get to the courthouse & the church (or in this case, the country club) on time. Complicating matters is the fact that Mary is confronted with two rather unwelcome visitors: her ex-husband (and baby daddy) Mark, & Ronnie Dalembert/ Mc Intyre – the con man Mary met & detested only a few months earlier. While Mark comes through for Mary, Ronnie manages to screw things up for everyone yet again. Only this time, things get really ugly for the Wit Sec team when, while escorting Ronnie to give his testimony, Mary, Marshall, Stan & Delia find themselves trapped in the courthouse & ambushed by assassins. ...

Mary's new witness Adam Wilson is blowing the whistle on his boss, a well-connected military contractor, & the stress is taking a toll on Adam's psychological health. When Adam's paranoia & hallucinations worsen, Mary & Marshall realise their witness might have gone off the deep end. But as they attempt to get Adam back to dry land & protect his justifiably alarmed teenage son Joey, Mary & Marshall begin to wonder if there might be some truth behind Adam's wild claims. After all, just because you're crazy doesn't mean they aren't after you. ...