The series picks up 1 year after Morgana's failed bid to rule Camelot and sees Arthur's evil half-sister make the ultimate sacrifice in an attempt to regain power. Meanwhile, Merlin is in torment after making a grave error that causes huge upset for Arthur. Guests include Nathaniel Parker as Arthur's uncle, but is he a relative to be trusted?
Follow link for high-res scans of SFX magazine August article about Merlin Season 4 (featuring the knights and an interview with Johnny Capps) with pictures & SPOILERS:
SFX: According to the SFX site, Colin's interview will be in the upcoming issue (Issue 213) that will be out on August 24, and Katie's interview will be in an issue when the series is broadcast.
-thanks to merlin-network for the info