“These characters have such huge futures ahead of them, which the audience knows but they don’t,” explains Colin Morgan, who portrays the warlock Merlin as a young man. “Merlin is vaguely aware of this new kingdom that will arise when Arthur is king, and the series is very much about how Merlin grows up and the decisions he has to make.”

In the penultimate episode of Season 2, Merlin made one of the most difficult decisions imaginable when he tried to kill Morgana (Katie McGrath), the beautiful ward of King Uther (Anthony Head), who had succumbed to the temptations of evil sorceress Morgause. Only Merlin realizes Morgana’s true nature, and when she returns in the first episode of the new season, she is keenly aware of what she views as Merlin’s deceit. That leads to a compelling conflict of darkness and light, which is at the heart of Season 3.

The attempt on Morgana’s life was “Merlin’s most shameful act,” Morgan says. “It was the lowest of the low, and that’s how he feels about it – so when she comes back after this yearlong search, every emotion he has felt toward her, the shame the guild from what he did comes floating back. And we quickly find out that she’s not very happy with Merlin. He knows that she is evil, that she has chosen that path, and Morgana knows that he knows all of this.” And yet, King Uther welcomes Morgana back with open arms, and Merlin’s status as a servant makes it impossible for him to voice his suspicions. “Things have hardened for Merlin. He has been hurt so many times by people he loves, by his friends,” Morgan explains. “It’s hurtful for him to see Morgana take that wrong path.” But it’s a path McGrath says she is excited to explore. “Not only is Morgana coming into  control of her magic and her powers, but she’s been with someone (Morgause) who accepts her for who she is. Now she’s coming back to make everyone else pay.”

Discover the magic and adventure of MERLIN when Season 3 debuts at Friday, January