Plot summary
The Storybrooke residents try to keep Arthur and the rest of Camelot from revealing their identities and prevent Emma from going dark as they search for Merlin, so Regina pretends to be the Savior in order to spare Emma the trouble. As the Storybrooke arrivals are feted at a ball in their honor, Percival catches on to the deception, attempts to avenge himself on Regina. In the ensuing fight, Robin is stabbed with Percival's enchanted sword, but David kills Percival. Regina begs Emma to save Robin, but despite Hook's plea not to, Emma does so, and results in Regina eventually paying the price.
In Storybrooke, the residents, and the now-transplanted Arthurians, are becoming fearful of Emma as the Dark One, and Regina must step up when a demon called the Fury attempts to take Robin's soul as payment, due to Emma having saved him on Regina's behalf. Meanwhile, Hook is feeling that Emma's good side is no longer there, while Henry meets a girl named Violet. It is revealed that Emma brought the Excalibur sword with the stone to Storybrooke, but she can't pull out Excalibur to make it whole unless she pays a price.
Credits
Adapted from Wikipedia contributors, Once Upon a Time season 5. HTML formatting and reference markers removed.