But soon Merlin finds himself in deadly danger - unable to trust even his closest friends, the boy wizard must expose the dark magic at the heart of Longstead's crisis alone! Merlin continues this Saturday at 8.15pm on BBC One!
> Merlin: 'Lamia' in pictures
> Merlin: 'The Secret Sharer' recap
Check out Digital Spy's ten teasers for this week's Merlin below:
1. "You're the one who holds the fate of this kingdom in the balance."
2. Merlin gets the chance to show off his medical skills...
3. "Merlin can't find his own backside most of the time!"
4. 'Lamia' is a big episode for the Knights of Camelot - we see a different side to each of them.
5. "The Knights are like brothers, yet they ******* and ***** like ****."
6. Cross-breeding can have dangerous consequences!
7. "Keep your mouth shut - or I'll shut it for you!"
8. One character's display of bravery surprises their friends.
9. "Don't think too hard - I wouldn't want you to hurt yourself."
10. Two characters unexpectedly come to blows.
What do you make of our teasers? Let us know below!