In the first episode we meet Mary Shannon a US Marshall for the Witness Protection Program. In this episode Mary tries to figure out what went wrong when a mobster's son who was under her protection is killed.

Mary learns that her witness, a NCAA basketball star, has a gambling problem

A member of the Program under Mary's watch is in a car accident and Mary has to find out if it was an accident or related to his former life.

Mary's paranoid witness wants to reconnect with his son.

Things get complicated when Mary takes on the case of Leo Billups. Leo saw his mother murdered and is going to testify against the people who killed her including his father.

Mary's assignment this week is Treena Morris a con-artist who is married to a diamond smuggler. After she is arrested by the feds, she decides to tell all on her husband and his friends. While Mary is trying to keep her safe, Treena gets engaged and her photo is all over the papers.

Mary works to solve the mystery of who tried to kill her witness, an art dealer. To complicate matters, both his mistress and his wife are in the program…and key suspects.

Mary suffers the consequences when an attractive witness, who she slept with, is accused of murder.

Mary briefs a new witness whose visitation rights with his son depend on the man's testimony. When Mary learns the boy is missing, she tries to find him.

A witness finds herself having difficulty in managing her own brood of children, so Mary offers to babysit the trio of problem kids.

Mary and Marshall find themselves in a difficult position when Stan's very first witness turns up dead and he is implicated in her murder.

The barely legal daughter of Mary's witness – a Miami racketeer – finds herself in a dangerous romance, just as Raph's mother visits to prepare an engagement feast for the surprised Mary.

When a Wall Street blue blood rats on his boss' investment fraud and hides out in WITSEC, something from his past life comes calling.

Mary and Marshall try to help FBI Agent Mike Faber convince his informant to enter WITSEC. Despite their best efforts, the informant refuses their protection and gets himself into a heap of trouble. After Mary, Marshall and Agent Faber save the informant from certain death, he and his family join Witsec.

A terminally ill father wants to reconcile with his children.

The closeness of a family is tested when they enter the program after the daughter witnesses a shooting.

Natasha, the mild mannered Ukrainian accountant, has gotten her new breasts, but her life becomes more complicated when she discovers that her new boyfriend is also in WITSEC.

When a series of murders seem to follow a new ex-con witness, including stabbing Mary's friend, she and Marshall have to figure out if he's the killer in time to save his next victim.

Mary’s new witness falls in love for the first time; Mary must stop her witness from taking out his pain in the form of an explosive device.

A beauty pageant queen finds out that she's spent most of her life in witness protection

A world-class counterfeiter witness is suspected in a murder; Mary and Marshall realize they may be hiding a witness from the government.

ATF agent Wade Guthrie is shot and left for dead by gun trader Jasper Malone. After three years in a coma, he wakes to find the world he left behind has drastically changed.

Mary's new witness is part of a mortgage fraud ring and is an important link in the case of FBI Agent Faber.

Mary works with an unapologetic con artist.

An Amish witness comes into the program and must learn to adapt.