In the installment, described as "Independence Day at the village green", the Doctor and his latest companion, Amy Pond, must save the world from a monster called Prisoner Zero.
Fans can also look forward to the Atraxi, a new intergalactic police, as well as the biggest Tardis in the programme's history.
At the launch, the co-stars discussed their excitement about the new series, with Karen explaining her particular fascination with her own character.
"What I love about Amy is that she has this feisty, independent, strong-minded exterior but underneath it all we know that she's actually this lost soul inside because of the way she meets the Doctor," she said.
The Scottish beauty even hinted at a romantic story line, revealing that her character will share a kiss with the Doctor.
Further fuelling hopes of an on-screen love affair, Matt reffered to Amy as the "sexiest companion that ever lived", and added that he and co-star Karen have great chemistry.
"We have grown very fond of one another," he said. "It's something we work hard at. I hope the tone of our relationship comes across as playful."
As for his role as the Doctor, which he took over after David Tennant's four-year run, the young actor couldn't be happier.
"To my mind it's the best part in British television. I'm fortunate to have it and I'm going to keep it."