In this universe, there is a group of people who hold a gene that allows them to travel back in time. The time traveling aspect is more of a plot device rather than an important factor of the story. The whole plot rests on the legacy of the time travelers. They are twelve people altogether, and are part of the similar bloodline. The person who carries the gene has been foretold back in time, and a secret society is in place to protect the time travelers and to educate them on their mission. The chosen ones travel back in time through a chronograph, and it was foretold that if the blood of all chosen ones are in the device, whoever holds it will amass a great amount of power. However, the original chronograph has been stolen from the society, thus starting the events of the trilogy.
Gwendolyn Shepherd and the rest of her family has always assumed that her cousin Charlotte was the carrier of the time travel gene. Instead, she ends up with the gene, and was immediately thrusted into training to fulfill the mission. She worked with Gideon, her male counterpart. During her travels, she was informed of a prophecy that she must uncover, and find out why these two people stole the original chronograph in the first place.
The book was set in London, thus the movie was also set in London. It's a bit strange to watch them speak in German while supposedly living in an English-speaking country the whole time, but that's not to deter the enjoyment of the movie. This does have a good set of supporting characters, particularly her best friend and the ghost they see roaming around the school. There is a lot going on, but it was just enough to keep the momentum of the movie.
This gives a good and concise introduction to the series. The movie does explain what the audience needs to know even if one hasn't read the books. It does have a great time travel fantasy story, and a conspiracy that plays out in the next two movies. However, I think it is also important that you like the main characters, since they would be the ones mostly appearing in the movies. I do suggest choosing one medium over the other. I had watched this movie before, just after reading the books, and was frustrated with it that I didn't bother continuing on with the next movie. Since I don't remember much from the books, I thought this would be a good time to continue on with the movies.
*Okay, maybe he pushed his attraction to her because they were each other's counterpart and somewhere in the society's rules says that they should date their counterparts. That's just wrong, considering their relations. I am obviously over thinking things.