The pressure is on for the creators and cast of Freeform's Shadowhunters after the first attempt to adapt Cassandra Clare's The Mortal Instruments fantasy novels was a box-office bomb.

Executive producer Ed Decter holds the reigns of the television version of Clary Fray's (Katherine McNamara) journey to becoming a demon hunter after her mother is kidnapped by mysterious forces on Clary's 18th birthday. The 2013 film version starring Lily Collins and Jamie Campbell Bower was widely criticized for omitting essential plot points in the book series and thus alienating the core audience.

The television series will allow more time to explore Clare's expansive fantasy world in depth. It's an ambitious venture for the network formerly known as ABC Family, as it launches its new brand with the Shadowhunters series premiere on Tuesday. Decter spoke to TVGuide.com about what's different this time around, what to expect and why he thinks they really got it right.

Why Shadowhunters the TV show and why now?

Decter: It really lends itself to television. It's really a no-brainer. Even the producers of the film will tell you that if they had to do it over again they would have gone right to television because the world is so big and there's so many moving pieces. It's so great to have all that for a television show when you want to have so many hours of it. Hopefully, we have 200 hours of it.

Shadowhunters stays true to the spirit of The Mortal Instruments

How do you decide what stays, what goes and what should be altered from the books

Decter: We have to say to ourselves, "OK, what are the fans expecting?" Then we have to say, "OK, what if you didn't know anything about this? Where would you start then?" We have to balance those two things. We're building in a lot of surprises for the fans, but ultimately they're going to be super happy about where we arrive. We're hoping that they go, "Wait a minute! Oh, I see what they did there."

The pacing of the show is different from the novels in some ways. Is that part of trying to surprise your core book audience?

Decter: The audience needs to know who the opposition is. Who is the villain here? If you withhold that, in a way, you don't understand Shadhowunters, like who are they helping? Who are they hurting? We don't know anything about this world. We tease the villain in the first episode, but he's so important and central to the story that we have to know what we call in the writing the inciting incident. What's the thing that's starting this story? Clary becoming aShadowhunter [is not] the only inciting incident.

Is there anything you're nervous about this very vocal fan base to see?

Decter: Every single person that has read the book is running their own movie in their head. They are running their own television show. Think of all the Harry Potter fans and what they were bringing to it. We have to make choices and tell a really good story for the people that are not fans and then satisfy the fans that they're going to get the things they want to see.

Katherine McNamara says Shadowhunters is darker than The Mortal Instruments

The first season roughly covers City of Bones, but how much of the subsidiary novels like The Bane Chronicles be involved in the series?

Decter: We really get details from the other things that Cassandra [Clare] has written. The whole arc of the first two seasons will basically be the first three books. In generalities, that's what you can expect. Book 2 happens in a week so it wouldn't be enough necessarily to fill a whole season.

How have the actors you've cast in these roles changed the characters and made them their own?

Decter: Initially, before we were casting people, they wanted us to cast the same people that were in the movie, who of course weren't available or were older now. Then [fans] very quickly, rapidly forgot about those people and these are the people they imagine in these roles. We think that the fans are going to be super excited about these actors portray it. Then we find out that the actors have a certain charisma or do certain things really well so we write more material like that for them. They can shine and shine within the character.

Everyone is pretty excited about the Magnus [Harry Shum Jr.] /Alec [Matthew Daddario] relationship -- how is that addressed in Season 1?

Decter: Episode 3, they meet for the first time in our show. We have an exciting and different storyline to get to the tremendous relationship that we can't wait to show the world.

Shadowhunters premieres Tuesday, Jan. 12 at 9/8c on Freeform.