Merlin - Season 1 Episode 6

Receiving tainted lilies collected by unsuspecting Gwen, royal ward Morgana falls ill with an unidentified brain disease Gaius can't cure. Mysterious healer Edwin's "remedy to cure all ills" seemingly works (by actually removing the cursed black beetle he hid in the lilies). As Edwin maneuvers grateful King Uther to instate him as new court physician, Gaius gets court archivist Geoffrey to allow him illegal access to the sealed records of Uther's purge of magic, revealing Edwin's parents as executed black sorcerers. After consulting the dragon (who says he must choose whether or not Arthur and Merlin's destined time has come), Gaius, taking a threat by Edwin to expose Merlin's magic, tells Merlin – the "son he never had" – that the time has come to step down. Edwin, now free to use another beetle, condemns Uther to an agonizing death like his parents but takes one monumental risk – a duel of magic with 'mere novice' Merlin.