Mary Shannon, a US Marshall of the witness protection program investigates the murder of a mobster's son which was under her watch. Meanwhile, Mary's birthday celebration finds her dealing with her dysfunctional family.
Mary is assigned to protect a drug dealers son, who had been adopted by another WITSEC family, when the father is released from prison and sues to regain custody. Although Mary realizes that the case revolves around an attempt to keep the son from testifying against his dad's boss, she struggles to prove it to the judge.
The high-profile wedding of a diamond smuggler has Mary posing as a bridesmaid.
When hit men sabotage their vehicle, Mary and Marshall find themselves trapped in the desert, with Marshall suffering a wound. Meanwhile, Jinx once again vows to clean up her act after discovering a painful truth about her past.
When an art dealer in which Mary is watching is shot dead, the prime suspects seem to be his wife and a mistress, who his wife knows nothing of.
One of a pair of brothers within the program, a basketball star, causes trouble when he develops a gambling problem.
After his daughter witnesses a gang murder, an arrogant doctor must move his family, and the once close clan is being torn apart by the stress of living within the program.
When a couple goes into Witness Protection, Mary finds them to be a handful when the husband goes missing without a trace. Now, finding him may be more difficult than keeping the couple safe from those who want them dead.
Mary's one night stand with a witness comes back to haunt her when he becomes the suspect of a murder.
Mary's witness, the mild mannered Ukrainian accountant Natasha, hits a roadblock in her new life when she discovers her new boyfriend is also involved with the WITSEC program.
After watching her mother's audition for "Sweet Charity," Mary is kidnapped. Meanwhile, Brandi's boyfriend, Chuck, is also abducted after two FBI agents are killed. When the Feds realize that there is a connection between the two kidnappings, Marshall and Stan help in a nationwide manhunt for both Mary and Chuck.
Following the kidnapping, Mary returns home to find that Brandi's involvement with Chuck may result in the end of her career. Meanwhile, Stan and Marshall try to find a way to get Spanky to tell the truth about Chuck's drug trafficking in order to clear both Mary and Brandi.
A dead witness causes Mary to take leave of her administrative duties to solve a "Ten Little Indians" story, until her plan gets changed by her own brand of Post-Traumatic Stress disorder.
Mary tries to get the testimony of a drug mastermind who gets high to control severe anxiety.
A witness finds herself having difficulty in managing her own brood of children, so Mary offers to babysit the trio of problem kids.
A witness becomes vulnerable to elimination by sniper after becoming trapped in a building collapse.
An Orthodox Jew enters Witness Protection, but his wife refuses to join him. The situation is made more complicated by the fact he is being pursued by a man motivated by a higher authority.
Mary and Marshall find themselves in a difficult position when Stan's very first witness turns up dead and he is implicated in his murder.
An engineer blamed for a bridge collapse enters the program after receiving death threats from family members of victims and being threatened by a government contractor who changed the materials used without the engineer's knowledge.
Mary and Marshall investigate a new witness they suspect may be responsible for a number of murders and the stabbing of one of Mary's friends.
FBI Agent O'Connor resurfaces to arrest Brandi for drug trafficking and murder. Mary is determined to uncover O'Connor's real motive for pursuing a case against Brandi.
Mary tries to locate the missing son of a witness who refuses to testify in court unless he is able to visit his child.
The teen daughter of a witness begins a reckless romance. Elsewhere, Raphael's mother visits Mary and starts planning her engagement party without her consent.
Mary lends her expertise for the U.S. Marshalls by making a training video with a film crew. Elsewhere, Marshall prepares the arrangements so that an elderly mobster in WITSEC can go to his son's funeral.
A counterfeit witness is implicated in a killing. Mary and Marshall feel the clues make no sense, and wonder if there is a conspiracy at hand.
After having revealed his bosses fraud, a Wall Street investor hangs out in WITSEC. He gives up his fortune to gain protection, which becomes inconvenient when a ransom from his past needs to be paid.
The US government helps a Latina political activist hide in Witsec, but the arrangement sours after she moves into her new home.
Even with her slow recovery, Mary's determination to track down the person who shot her gives her a boost that she needs to fight through and do her job when an ex-con wants to reconnect with his son.
Back in 2003 when Mary met Marshall for the first time, they were both attempting to get lovers Claudia Tobin and Henry Doer into a WitSec program. However, it's confusing if it's Claudia and Henry's relationship or Mary and Marshall's relationship that's going to last.
After being left for dead and being in a coma for three years, ATF agent Wade Guthrie comes back after being shot by gun trader Jasper Malone to find out how the world has changed since he left.
When an FBI informant refuses WITSEC protection, he gets deep into trouble. Stan is forced to treat a witness with suffering from pugilistic dementia and sees what he can do for him.
Mary fears that her witness, Dominic, is not going to handle a rejection well when he finds his new love, explosives. The office gets a new Financial Manager and Mary says her goodbyes to Raphael.
When a witness gets paroled, he has a hard time acclimating to life outside the prison. Marshall lends a helping hand when Mary's witness is victim to revenge.
Mary gets a new witness who has information on FBI Agent Faber, a man from Mary's past, when he is part of a mortgage fraud ring.
Seth Mann, Marshall's father comes and works on "Operation Falcon", a sweep of open warrants. Brandi returns to Albuquerque with a story that Mary is weary about and a new quest from her past.
When an organized crime wife sees that her niece is repeating all of her mistakes, she seeks asylum with WITSEC. However, her "secret weapon" puts her in danger and turns to Mary for help.
When a witness who has Aspergers and no social filter refuses to testify, Mary has to try a new approach. Marshall and Stan have to find out why an Immigration and Customs Enforcement agent is keeping one of their witnesses and threatening deportation. Brandi tells of her plans of the money that she invested with Scott.
When a homeless man sees a pipe bomb plot, he goes into the program, but has a hard time with the rules. Mary agrees to search out his birth parents. Brandi says that she has had enough of Scott when he asks her for money.
When a 16-year-old witness rebels, Mary is forced to play the "stepmother" and is not too happy when her real parents don't see the issues. Marshall deals with a witness whose brother told his location. Brandi takes care of Scott, her brother, after her is beaten up.
After a priest witnesses the murder of a stripper he joins and gives up his priesthood with no problem. However, he doesn't want to stop seeing the stripper's family. Meanwhile, Stan tries to find the right words to tell a daughter of a witness that her father wasn't who he said he was. Brandi decides that she will move in with Peter.
When Mary uses a car thief to catch another thief, she gets to know a little more into the crime business. All this is to clear Brandi from Grand Theft Auto too. Brandi gets engaged to Peter.
A WITSEC witness need to reconnect with his son, but suffers from paranoia that someone is going to come and get him. However, when things come true, Mary and Marshall have to work fast if they are going to be able to protect their witness.
When a Financial clerk sees a murder happen in front of him, he is forced to enter the program, but refuses to take down his friend's wife, who he is madly in love with. In Romeo and Juliet kind of love, these two star-crossed lovers will do anything to be together.
When a teenage pageant queen realizes that her mother has been in WITSEC all of her life, she takes the news hard. Mary intervenes to help the beauty queen to realize that it is a good thing. However, things are not what they seem.
A Con-Artist enters the program and Mary makes it her mission to uncover that he is still at it despite his telling. However, he has an ace up his sleeve. That is his confession to take down even more dangerous players in the con business.
When an Amish couple enter the WITSEC program, Mary and Marshall have to try to teach them all about the culture of the "real world" and keep everyone safe.
Mary gets a witness who is terminally ill and reaches out to his family despite his objections to see if he can reconnect with his estranged children.
Mary is in charge of a Hindu family with strong traditions. In order to keep everyone safe, she counsels a divorcing couple in WITSEC. In the process, Mary learns about Hindu tradition so that she can bring the family closer together rather than apart.
When Mary and Marshall have to watch a Witness and his brother, one is not happy at all to be giving up his comfortable lifestyle. However, it proves more tough when they have to protect them from one another as well.
Stan and Marshall are in charge of watching a teenage rock star and her over-demanding mother and Mary has to deal with a witness who has gotten in touch with his spiritual side. Mary also looks at possibles for people to adopt her baby.
Mary is in charge to protect an Army vet from a military lawyer. Mary also gets a visit from Mark about the baby.
When a pregnant courtesan is in danger from a gangster, Mary steps in to protect her from harm. Mary takes a class that teaches her about childbirth, but she doesn't know if she can trust her though.
On the day of her sister's wedding, Mary is flown to Miami in order to protect her least favorite witness from hired mercenaries.
Mary returns to WITSEC from maternity leave to find a new set of office dynamics. Plus, she must protect a witness who could take down one of the most powerful secret societies in the country.
Mary scrambles to find child care while working on a case in which a hoarder witnessed a violent murder.
When Marshall's witness escapes from the WITSEC offices and disappears on an Indian Reservation, Mary and Marshall will need the help of a Native American detective to track him down.
Mary looks after a bigamist, who's hiding from his former employer and his two wives.
Mary must prevent a drag queen from reverting back to his old ways, meanwhile Marshall is brought into an undercover sting operation.
When Mary's fugitive father turns up, his return puts Brandi and Jinx in danger. Revelations abound as Mary struggles to determine whom she can trust.
The FBI keeps an eye on Mary after her father goes on the lam seeking vengeance. Mary tries to lose the agents tailing her in order to track her father down herself.
In the series finale, Mary finds herself caught between her "model" witness and an unexpected family reunion, while radical changes take place around the WITSEC office.