[1][2] Sam leaps into various points, over a six year period, in the life of Lee Harvey Oswald (Willie Garson) in an effort to seemingly prevent him from killing President John F. Kennedy or find the truth about the events that day.

Sam finds his patience tested when he leaps into Nikos Stathatos (Socrates Alafouzos) in a lifeboat with a bratty, self-obsessed heiress Vanessa Foster (Brooke Shields) and end up stuck on an island from which they will not be rescued for nine years.

Sam leaps into Leon Stiles (Cameron Dye), a dangerous criminal who has taken Carol Pruitt (Connie Ray) and her young daughter, Becky (Beverley Mitchell), hostage.

A female quantum leaper named Alia (Renée Coleman), aided by observer Zoey (Carolyn Seymour), is apparently there to "put wrong what once went right".

Sam leaps into a small Louisiana town as a sheriff named Clayton Fuller (James Whitmore Jr.) who's also the father of 10 year old Abigail Fuller (Kimberly Cullum), a girl accused by local townswoman Leta Aider (Mary Gordon Murray) of killing her husband and daughter, even though the daughter was never found and the town doctor (Max Wright) confirms the husband had a heart attack.

Deputy sheriff Bo (Stephen Lee) and the doctor's son, Will (Travis Fine), both help protect Abigail from Leta's attacks, though Sam must save his host and Abagail from dying in a house fire.

Sam also carries out his original mission, getting Dr. Ruth's radio coworkers, Doug (Peter Spears) and Debbie (Anita Barone), into a lasting relationship.

Back in the PQL's waiting room, Dr. Ruth helps Al deal with his fear of abandonment (raised in an orphanage, divorced by Beth) and his inability to tell Tina that he loves her.

As nerdy college kid Arnold Watkins (Tristan Tait), who dresses up as a superhero, Sam must stop Mike Hammond (Neil Patrick Harris) from operating dangerous chicken races as part of his fraternity's initiation ritual.

However, the sudden return of Evil Leaper Alia (Renée Coleman), and her observer Zoey (Carolyn Seymour), makes the task significantly harder.

Leaping into Elizabeth Tate (Cynthia Steele) in a women's prison, accompanied by former Evil Leaper Alia (Renée Coleman), who has leapt into fellow inmate Angel Jensen.