Hmmm... Merlin seems to be alternating between really good episodes and "meh" episodes (last week's) lately, and this was another good one!
Although she still doesn't know Merlin is "Emrys" (and thus her mortal enemy), Morgana does realise he has done a lot to protect Arthur and foil her plans on many occasions and so finally launches a direct assault on him as a prelude to a plan to assassinate Arthur. She knows him well enough to find the perfect lure for a trap and he falls for it hook, line and sinker! Took me a while to see it coming and there were some moments that truly surprised me and had me going "woah!". Merlin really had me worried there!