[s4e7] The Secret Sharer -

: A young, inexperienced sea captain discovers a man named Leggatt clinging to the side of his ship. Leggatt has killed a man in self-defense and is fleeing justice.

: The episode title refers to the bond formed between Merlin and Alator; after Alator realizes Merlin is the prophesied Emrys, he chooses to protect the secret and sacrifices his alliance with Morgana to keep Merlin’s identity hidden. [S4E7] The Secret Sharer

: Morgana teams up with a powerful sorcerer named Alator of the Catha to kidnap and torture Gaius, believing the physician knows the truth about her arch-enemy. : A young, inexperienced sea captain discovers a

If you are looking into the literary origins, this 1910 short story is a staple of psychological fiction. : A young