Gemma Hart never knows when her father is going to whisk her back in time. Her toes start tingling and she has a few minutes to find a secret haven where she can disintegrate and appear in another time and place. While “across the line,” her training and skills are put to the test as she completes a mission that will change history for the lucky few her father has selected. Gemma's parents are adamant that secrecy is paramount to her family’s safety. If people knew what they were capable of, they could be "used and abused", as her mother always says. Afraid she might accidentally utter the truth and break the ancient oath of her people, Gemma spends her school days as a loner. Only one thing can throw her sheltered life askew... Harrison Granger. Harrison never expected to talk to the strange Hart girl, but after a brief encounter he can't stop thinking about her. He begins a campaign to chisel away her icy veneer and is met with unexpected consequences. As he slowly wins this girl over, he enters a surreal world that has him fighting to keep his newfound love and his life.

Gemma's parents have put enough rules around her relationship with Harrison that she feels like she's living on parole. But she wins one battle—a summer job working for Harrison's step-father. It is the perfect chance to spend the steamy, hot Florida days with her boyfriend. It's also a great distraction from the cellphone hiding in her underwear drawer—her only contact with Gabe, the mystery man who's stalking her. When she confronts Gabe, he tells her that her parents are not who she thinks they are, and Harrison has the gall to believe him. Surrounded by conflict, Gemma doesn't know what to believe, and it takes a trip back in time for her to glimpse the sickening truth. Thanks to her parents, she returns to the present to find the love of her life no longer exists. His family line was broken and now, so is she. This betrayal forces her to seek out Gabe. Setting aside her fear of the truth, she must trust this man and learn what he can teach her... otherwise, she'll never get her boyfriend back.

It is only a matter of time before Gemma's parents find out she traveled through time to bring Harrison back into existence. The fear of being found out is a heavy weight on her shoulders, but she refuses to give up on everything she's fought for. Harrison is worth the risk. The couple draws closer together as they battle opposing forces from all sides. They stay strong until Gemma's parents welcome an exchange student into their home. Simeon, a gorgeous Californian, is as smooth as coffee and, supposedly, a fellow time spirit. Gemma's parents expect her to take him everywhere and, of course, fall in love with him. After all, he is the boy they have chosen for her. No longer able to sneak off alone, Gemma must watch every step as she waits for the inevitable nightmare to catch up to her. Her parents ultimate goal is to get that last necklace and open the box hidden in their safe. If they do, Gemma knows her entire world will unravel. As the danger mounts, Gemma must decide if she has the courage to make the ultimate sacrifice to save the ones she loves and stop to her parents' destructive plans.