An unexpected whistleblower returns to tonight’s Once Upon a Time season 5, episode 3, “Siege Perilous.” Find out who cannot be trusted!

Camelot is not what it seems on Once Upon a Time. The burdens of the king, and in Storybrooke’s case, the sheriff, are heavy and not to be carried alone. So when King Arthur and David pair up in both Camelot and Storybrooke all the problems they face seem to become much easier to bear.

But Once Upon a Time is not for those who enjoy a straightforward narrative. “Siege Perilous,” tonight’s episode title refers to a seat at Arthur’s roundtable reserved for the one who carries out the most sacred quests. It has remained empty since Lancelot left the kingdom and according to Arthur will remain empty for quite some time.

When David and Arthur find themselves with two extreme quests on their hands and no one to turn to for assistance, it appears that the stars aligned in their favor. But one of them has less than desirable intentions. And a third party is there to break up Once Upon a Time‘s latest bromance.

Camelot: The quest for the Crimson Crown

In Merlin’s tower David is itching for an adventure that does not require rocking Neal Jr. back and forth. When Regina stumbles upon a mushroom, err toadstool, called the Crimson Crown that may allow them to speak with Merlin through his magical entrapment, he leaps at the opportunity to go on the quest into the Eternal Night Forest.

Arthur, perhaps a bit over being a part of the welcoming committee, offers to suit David up and accompany him into the woods. The two are fast to bond, and almost too much alike for comfort. But David is finally feeling a kinship to someone with a similar uphill struggle. Do they really want to be the men who are remembered for the woman they kissed or for the quests they went on?

A peasant and shepherd battle a rickety bridge to cut free the single toadstool that will both save Emma and Camelot. Along the way back from the mossy hill, however, David must battle an army of undead armor that get the better of him. Arthur is there to lend a hand and pull him free from the lake, but they lose the toadstool in the process. Feeding David the line, “the word quest means to seek not to find– it’s the seeking that matters,” they laugh both disappointed that they are heading home empty handed. But Arthur has another surprise in mind for David. It may not be a toadstool, but this seat may be much more comfortable.

Storybrooke: The quest for the Relic Chest

David is getting restless and taking it out on office chairs in the sheriff’s office. No matter what he tries to do, nothing is working fast enough to protect his daughter and restore a sense of safety to his town. What he needs is a purpose and Arthur may be able to help. A chest made its way back to Storybrooke containing all the relics collected by the Knights of the Round Table on their quests. It turned up empty.

Finally utilizing his quick thinking, David takes a relic from Gold’s shop, a commemorative mug from Doctoberfest that he waves over the amassed crowd claiming it has the power to pull the truth from those who drink from it. The thief will be caught, if he does not flee first–which the squire of Arthur’s court does.

Jumping in the truck David chases after the man with Arthur in the passenger seat. The squire requires a more forceful shove to come to a halt. David hands the steering wheel over to Arthur and climbs into the bed of the truck with a plank of wood and jousts the man off of his horse. Although they did not recover all of the items, David and Arthur formed a bond and stumbled upon the Crimson Crown along the way. Arthur, not quite sure what the mushroom is, allows David to take it and he presents it to Regina. He is at least the hero in his friend’s eyes for the day.

Lancelot: The quest of the whistle blower

Mary Margaret looks on at David with a smile as he accepts his new seat among the honored Knights. But one person in Camelot suspects foul play and grabs Mary Margaret’s attention. Lancelot is not quite as dead as everyone believes.

Arthur painted Lancelot as a man who tortured himself greatly over the situation between himself and Guinevere. Arthur, however, remained the humble, forgiving man who wished his old friend nothing but a life of happiness outside of Camelot. But Lancelot has another story to tell and it is one of corruption, greed, and a ruthless leader who will do anything under the flag of serving his kingdom.

Arthur may have saved David’s life, but he also stole the Crimson Crown for his own protection against the new intruders. And in Storybrooke a similar story unfolds– Arthur throws his squire under the horse and forces him to take the blame for stealing their chest and the relics within. Locked away from the town, Arthur coerces the loyal servant to drink a poison in the name of Camelot. Once he dies, a new Camelot will be erected in his honor and that Camelot will be in Storybrooke.

Once Upon a Time season 5, episode 4, “The Broken Kingdom,” airs Sunday, October 18 at 8:00 p.m. ET on ABC.

What do you think of ‘Once Upon a Time’s’ latest twist?