Fantasy drama Merlin returns to BBC One next month with a fourth series, kicking off with a two-part opener.

The first episode sees Merlin face his toughest challenge yet when Morgana’s blinkered determination threatens not only Arthur’s future, but also the very balance of the world. With her magic stronger than ever, the sorceress summons the mighty Callieach to tear open the veil between the worlds.

> Order the Series 4 Volume 1 DVD on Amazon.

‘The Darkest Hour’ airs at 7.50pm on Saturday 1st October on BBC One. In the meantime, here are ten teasing lines of dialogue from the episode…

» ‘What’s in the cart?’

» ‘Arthur is going to kill me.’

» ‘His heart is broken and his spirit is gone.’

» ‘For months; nothing. Why now?’

» ‘They were there, but they weren’t there.’

» ‘I don’t know how I’d have got through the last few months without you.’

» ‘Merlin, do you need your comfort blanket?’

» ‘It’s not you fault.’

» ‘No mortal has ever survived their touch.’

» ‘Promise me you’ll look after him when I’m gone…’