In an effort to protect Emma, Regina steps up in a surprising way that will test her mettle as a force for good. King Arthur and Queen Guinevere throw a royal ball to welcome the heroes to Camelot, but when the celebration takes a deadly turn, David and Robin must leap into action or lose a crucial asset in the fight to save Emma. Back in Storybrooke, Hook deploys a tried-and-true technique in hopes of bringing his Dark Swan back into the light while the heroes discover that some unexpected baggage has followed them home from Camelot.