Two roads diverged in a yellow wood, (слэш)

Title from the Robert Frost poem.
Carrying on from the last episode in a different way.
Merlin manages to get Arthur to the Isle of Avalon before he dies. But saving his life means sending them both into an alternative version of their past, where Merlin finds he can’t use his magic and where the Arthur of that world has apparently been missing for the last three months.