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Doctor Who will kick off the new series with one of its darkest ever plots as Peter Capaldi’s Time Lord ponders whether to murder a child.

The dramatic season opener is based on a line muttered 40 years ago by Tom Baker’s Doctor in Genesis of the Daleks.

At the time, he asked: “If someone who knew the future pointed out a child to you and told you that child would grow up totally evil, to be a ruthless dictator who would destroy millions of lives, could you then kill that child?”

Capaldi’s nightmare unfolds after the Tardis takes him to a battlefield where he realises he is face to face with a younger version of his arch-enemy Davros, who went on to create the Daleks.

The dictator, played as a grown-up by Julian Bleach, was last seen in 2009 when he locked horns with David Tennant’s version of

The Doctor.

poll loading Who is the best Doctor of recent times? 1000+ VOTES SO FAR Peter Capaldi Matt Smith David Tennant Christopher Eccleston

This time he returns to Dalek planet Skaro and holds the Time Lord captive as he struggles to save the evil machines from dying out.

Despite the dark start to the ninth series – which airs later this year – show boss Steven Moffat insisted he has made the Doctor more light-hearted.

He said: “I’m writing quite funny this year. Peter magnifies anything dark. So I’m pushing him the other way. He’s also got a Scottish gloom about him.

“It was great fun to do for a year, but that’s not how we’ll play the rest of him.

"As ever, Doctor Who is a combination of complete daft silliness and loads of people getting slaughtered in the early evening.”