Apparently, the aliens will be hell-bent on Earth's destruction and only the Doctor and his companion can stop them.
Apparently ''The producers wanted Matt to end his first season as the Time Lord with something explosive and exciting. And this fits the bill.''
“It’s got all the right elements for a great finale and plenty of opportunities for cliffhangers, with fans not knowing who survives.”
The series is still set to start in the Spring (I just wish they'd settle for a date already but the BBC has never been fast at giving information).
On the other hand, it appears that Torchood will return only on the net. Which I think would be a serious let down of the fans.
Still, take all this with a grain of salt.