Once Upon a Time's Josh Dallas teases dark turn for David 

Now that his daughter is back in Storybrooke, David will turn his focus to more pressing matters in Sunday’s episode of

With the help of Hook (Colin O’Donoghue), David (Josh Dallas) sets out to uncover the truth about what really happened to his late father, with a blast from his past kicking him off on this journey. “He’s visited by the ghost of his father that urges him to push forward to find out exactly what happened,” Dallas tells EW.

The visit couldn’t come at a more inopportune time. David’s lack of sleep and the fact that he’s now long been separated from his moral center Snow (Ginnifer Goodwin) means David is ruthless in his determination to get at the truth. “He’s gone through his whole life thinking that a story he had heard his whole life was the truth, and all of a sudden he found out that it wasn’t the truth, that there was a different story,” Dallas says. “So somehow it might change his story, and how he feels about himself, how he feels about his life, how he feels about his father, how he feels about being a father, how he feels about being a husband, all of that stuff. So he’s super determined to figure out the truth.”

“It’s forcing him to go really dark,” Dallas warns. “On his quest to find out the true story of what happened with his father, and the true story of who his father was, he gets so caught up in that madness that he’s almost willing to go to really, really dark places.”

While Snow is unable to help her husband, Hook is on hand to keep David from going over the edge. “The one person that pulls him back from that is Hook,” Dallas says. “Hook and David create a whole different part of their friendship, and their bromance, and there’s a newfound respect because — particularly during that period when he’s crazed with this madness of finding out who really killed his father — Hook is actually being the hero.”

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The hour also features flashbacks to young David and James, revealing how the twins were split at a young age — expect Alan Dale’s return as King George on Sunday! “We go way back into why David’s father gave up his brother, and we find out the real reasons,” Dallas says. “We find out that maybe he thought it was a mistake, and maybe he did try to make things right, which is also another big piece to the puzzle for David in finding out that his father wasn’t what he thought, that maybe he was a good man, and he was just trying to do his best.”

As for when Snow and Charming will finally be reunited, awake from the sleeping curse at the same time, Dallas is staying mum. “They don’t get out of it easily,” he offers.

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