"The Broken Kingdom" is the fourth episode of the fifth season of the American fantasy drama series Once Upon a Time, which aired on October 18, 2015. In this episode, Mary Margaret decides to take matters into her own hands when she fails to convince David about Lancelot's warning about King Arthur, and Hook’s unwavering love for Emma provides a slight possibility of succeeding in her struggle against the unrelenting voice of Rumplestiltskin, while in Storybrooke, Emma unleashes a weapon to unleash Excalibur by using a brave soul to do the task. Back in Camelot's past, Guinevere sets out with Lancelot on a quest to locate the other half of Excalibur, as she begins to sense Arthur's obsession with making Excalibur whole.