"Once Upon a Time" season 5 episode 3 ended with Lancelot (Sinqua Walls) coming back after his apparent death to warn Mary (Ginnifer Goodwin) that King Arthur (Liam Garrigan) could not be trusted and that the king had a secret scheme against Storybrooke, a scheme that will put Emma's (Jennifer Morrison) life on the line.
Episode 4, titled "The Broken Kingdom," will see this problem explode as King Arthur goes up against Mary, David (Josh Dallas) and Lancelot. It was previously revealed that Arthur's true intentions were to use the Dagger and Excalibur to change Storybrooke into a new Camelot.
The official promo for the episode shows Arthur telling David, who is now an official member of the Knights of the Round Table, that the sword Excalibur is not whole. Not only that but the missing piece is actually the Dark Dagger. At the same time, Emma continues to be guided by the malicious Rumplestiltskin (Robert Carlyle).
Mary is taking matters into her own hands after David initially refuses to believe that King Arthur is their greatest threat and that his plans may not only keep Emma in the darkness but it may also end up killing her.
As stated in a report from the IBTimes, Emma has been doing everything possible to not use her dark powers since this may cause her to further lose herself to the darkness. However, the voice of Rumplestiltskin might force her to user her powers or do something she will later regret and it is speculated that her actions will cause her to lose her memories.
The trailer then ends with David, Mary and Lancelot crossing swords with King Arthur where he demands they hand over the Dark Dagger to him. The heroes know that they need both weapons to save Emma but in doing she may also be killed but they also cannot let King Arthur destroy Storybrooke.
"Once Upon a Time" season 5 episode 4, "The Broken Kingdom," airs this Oct. 18.
