The battle to return Emma (Jennifer Morrison) to the light continues in Season 5, episode 4 of “Once Upon a Time.” It’s been a long and confusing journey so far as fans struggle to figure out what exactly happened to turn her dark. However, more answers will be revealed in Sunday’s installment, titled “The Broken Kingdom.”

According to the synopsis for episode 4, Mary Margaret (Ginnifer Goodwin) will quickly figure out that their biggest threat in helping Emma is actually their new ally, King Arthur (Liam Garrigan). Mary Margaret was able to get the heads up from Lancelot (Sinqua Walls), who was believed to be dead. However, David (Josh Dallas) is not convinced that their new friend is a danger to them. Now that he’s a Knight of the Round Table, will his allegiance to King Arthur cloud his judgment? Whatever the case may be, Mary Margaret is ready to “take matters into her own hands.”

OUAT Lancelot Lancelot (Sinqua Walls) will warn the Storybrooke heroes about Camelot in Season 5, episode 4 of "Once Upon a Time." Photo: ABC

Meanwhile, a flashback to Camelot will shed more light on King Arthur’s relationship with Lancelot, the knight who once sat in the Siege Perilous chair. All fans know so far is that Lancelot betrayed King Arthur by pursuing his wife, Guinevere (Joana Metrass). But it sounds like there is more to the story. The episode description teases that Guinevere felt that her husband was “losing his way” after becoming obsessed with making Excalibur whole. In an effort to help her beloved, Guinevere set off with Lancelot “into the heart of darkness” on her own quest.

OUAT Episode 5, 4 Guinevere (Joana Metrass) may love King Arthur (Liam Garrigan), but episode 4 of "Once Upon a Time" will reveal that they hit a rough patch in their relationship. Photo: ABC

Love makes you do crazy things, and viewers will see that between Emma and Hook (Colin O’Donoghue). The synopsis adds that Hook’s “unwavering love” for Emma will give the new Dark One “a glimmer of hope in her struggle against the unrelenting voice of Rumplestiltskin (Robert Carlyle).” However, that doesn’t mean that she’s not trying to make Excalibur whole in Storybrooke. She’ll unleash her “secret weapon” as part of her plan to get the “brave soul” to pull Excalibur from the stone.

“Once Upon a Time” Season 5, episode 4 will air on ABC on Sunday, Oct. 18 at 8 p.m. ET.