Michelle MacLaren tells THR about her landmark episode and teases what's to come Sunday: "I was so blown away."

Update: Read our full chat with director Michelle MacLaren here.

Director Michelle MacLaren and the Game of Thrones team threw loyal book readers for a loop last week with the first episode of the HBO series to stretch significantly beyond George R.R. Martin's novels.

In the final moments of the episode, we were taken beyond the Wall to finally discover what the White Walkers have been doing with Craster's sons all of these years.

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"I was so blown away to find out what they are doing with the babies. I thought 'Wow.' I was very excited to do that," MacLaren tells The Hollywood Reporter of learning the key plot point. She also admits with a laugh: "I had thought they ate the babies – isn't that horrible?"

The revealing scene presented more questions than answers, and that was intentional. MacLaren says showrunners David Benioff and D.B. Weiss were very particular with what they wanted to reveal in the episode.

"We saw very little of the White Walkers other than the one on the horse. There's a lineup of blurry figures and we pull back over the baby," she says. "Presumably those are White Walkers, but we left that somewhat of a mystery on purpose."

MacLaren, who also directed this Sunday's episode, remains tight-lipped on what future excursions beyond the book there may be.

"Dan and David are such great writers. It's exciting to see where they are going to go moving beyond the books, which is starting to happen more and more," she says.

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MacLaren is known for directing some of television's most buzzed-about hours, including last season's "The Bear and the Maiden Fair," March's Walking Dead season-four finale and Breaking Bad's classic "One Minute."

As for what's to come on Sunday, there isn't much she can say, other than one scene was shot in "the deepest mud" she's ever seen, and that one of her stars was so adept with a blade that he didn't need the stunt double who was on hand during a key sword fighting sequence.

Check back to THR.com/GoT Sunday night for a spoiler-filled postmortem with MacLaren about the episode. For now, read our theories about what's to come here.

Email: Aaron.Couch@THR.com

Twitter: @AaronCouch