The Winter King episode 9 reveals that Arthur had druidess Nimue banished to the mythical Isle of the Dead, but what exactly is this place?
Warning: Major spoilers for The Winter King season 1 episode 9 and The Warlord Chronicles books below!
This was following a nasty feud with some Christians in Avalon, but given Nimue's belief in pagan magic, they were never destined to be friendly. Still, Derfel is shocked by Arthur's decision and by the end of the episode, he defies orders and rides for the Isle of the Dead to rescue her. This doesn't sound like it will be an easy task either, as those who enter the Isle are said to never return.
Both the series and the book make it sound like once a prisoner enters, they never come out again. This is what makes Derfel's defiance and willingness to risk his life to save Nimue such a big deal, but once he gets inside, he may find his mission is even harder than he realized.