5x07 Emma & Hook 

EMMA AND MERLIN EMBARK ON A PERILOUS QUEST TO RETRIEVE PROMETHEUS' FIRE FROM THE BIRTHPLACE OF DARK MAGIC, ON ABC'S "ONCE UPON A TIME"
Elliot Knight Guest Stars as Merlin, Liam Garrigan as King Arthur and Joana Metrass as Guinevere
"Nimue" - In Camelot, Merlin spearheads a mission to reunite the dagger with Excalibur so he can use the weapon to save Emma from the darkness threatening her soul. With Zelena in tow, Hook, Mary Margaret, David, Regina and Robin steal into Arthur's castle to take the broken sword from the maniacal king. Meanwhile, Merlin brings Emma along on a journey to confront his ancient nemesis and retrieve the sacred spark he'll need to reforge Excalibur. Both parties are tested, but one suffers a blow that could derail the entire operation. In a flashback to long before the Age of Arthur, young Merlin finds purpose after he is blessed with magic and immortality, but when he falls in love with a young refugee named Nimue, everything changes for Merlin, as their romance starts a chain of events that touches every one of our present day heroes, on "Once Upon a Time," SUNDAY, NOVEMBER 8 (8:00-9:00 p.m., ET) on the ABC Television Network.