'Once Upon A Time' season 5 spoilers (ABC): Mary Margaret learns the truth about King Arthur in episode 4 'The Broken Kingdom'

Once Upon a Time season 5 Facebook/ OnceABC

This week's "Once Upon A Time" season 5 episode will reveal King Arthur's true intentions. Titled "The Broken Kingdom," Mary Margaret learns from Lancelot that the king, who presents himself to them as an ally, is nothing but a traitor who wants the dagger for himself.

Mary Margaret tries to tell Charming about it but her husband seems to be too blinded by the fact that he now has a seat in the Knight of the Round Table, which is offered to him by the same person accused of being the bad guy. This leads her to "[take] matters into her own hands."

It remains to be seen what Margaret will do to expose the evilness of King Arthur to her husband and to the rest of the heroes, but fans could only hope it won't be something that will put herself in danger. Also, whatever this plan is, could it still involve Lancelot, who is now presumed dead?

Meanwhile, the upcoming "Once Upon A Time" season 5 episode will check in on Camelot, where a flashback sees Guinevere on a journey to the "heart of darkness" after she realizes that Arthur is so consumed by the Excalibur that it has gone so far as to change and destroy him.

Lastly, the installment follows Dark Emma, who stole the axe of one of the dwarves in the last episode in order to retrieve the sword from the stone. But she wasn't successful. In a sneak peak for the episode, Rumple talks her into getting the dagger, which is located in Regina's room.

The synopsis for the "Once Upon A Time" season 5 episode reveals that Emma will unleash her "secret weapon" to locate the hero that will be able to pull out the Excalibur out of the stone. Could the dagger be this "secret weapon"?

In "The Broken Kingdom," viewers will also see Emma recognize the voice of Hook over that of Rumple's, thanks to the steadfast love of Hook for the woman of his dreams.

"Once Upon A Time" season 5 episode 4 "The Broken Kingdom" airs on ABC on Oct. 18 at 8 p.m. ET.

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