Mortal Instruments fans, get ready -- Shadowhunters star Katherine McNamara (Clary Fray) says the TV show has a lot of hidden surprises for you to uncover.

“If you love the books, it's worth a watch, because we have lots of lines and scenes directly from the book,” McNamara tells ETonline. “We have Easter Egg props hidden all over that -- if you know the books -- things will make sense to you. And if you don't know the books, we have the time and explain it in a way that really makes sense, but still keeps the story moving.”

WATCH: Shadowhunters Stars Reveal Why You Can't Miss This 'Dark' and 'Sexy' New Show!

We caught up with the 20-year-old actress at the premiere of Snervous, just about a month before her new show debuts on Jan. 12 -- the same day its network, ABC Family, becomes Freeform.

“We are flipping the switch,” McNamara jokes.

The Shadowhunters crew is also flipping the script a little bit. While McNamara promises the TV show will be truer to the book series than the 2013 big screen adaptation starring Lily Collins, there will be a few changes.

“You know, our TV show takes kind of a new interpretation,” McNamara teases. “Different from the books. Different from the film. And what's great about it is, we have an opportunity with the television interpretation to take kind of a new perspective on the show, and to be a little darker, and a little grittier, and a little more intense.”

MORE: Shadowhunters Sneak Peek: Clary Is 'Ready' to Accept Her Demon-Hunting Destiny!

“We basically have in the first season the same story as the first book,” McNamara continues. “From point A to point B, we pretty much do the same thing. But the way in which we get there, we changed a few things, because we want to make it exciting for people who know the books cover to cover, and people who are new to the world.”

McNamara says they definitely stay true to the characters; she dyed her hair “carrot red” for the role.

“But then we bring in books, or characters, from books two, three and four,” McNamara says. “And then we bring in characters that don't even exist in the series.”

WATCH: Pretty Little Liars' Stars Spill on New 'Big Bad' After the Time-Jump

Judging by online excitement, fans can’t wait for the premiere -- and McNamara can’t wait for them to see it, saying she’s prepared for Pretty Little Liars-style fandemonium.

“I’m ready,” McNamara says. “I'm so excited to share this experience with them, and with the cast, and with everybody that's been involved in the production ... I'm really excited for people to see it, and I'm ready to share it.”

Check out ETonline’s exclusive first look at the new show in the video below.