: 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.
: The story explores the "double" or "doppelgänger" trope. The Captain sees himself in Leggatt and hides him in his own cabin, risking his command and his ship to help the fugitive escape.
: 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. [S4E7] The Secret Sharer
In this 2011 episode, the central conflict revolves around Morgana’s desperate quest to uncover the identity of "Emrys" (Merlin’s true self).
: 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. : The episode title refers to the bond
If you were expecting a Star Trek guide for a Season 4, Episode 7, the corresponding episodes are: "Merlin" The Secret Sharer (TV Episode 2011) - IMDb
If you are looking into the literary origins, this 1910 short story is a staple of psychological fiction. : A young, inexperienced sea captain discovers a
: Critics often praise this episode for its darker tone and the emotional scene where Arthur expresses his fear of losing his few remaining friends. 2. Joseph Conrad's "The Secret Sharer"