Written by author Simon Messingham and read by series star David Tennant, it features the Tenth Doctor travelling alone.

Charlie explains that humans used a process dubbed Global Cooling, refreezing glaciers.

Karl Baring started work on growing new crops, but so far, hasn't succeeded – running out of money, depending on charity.

He tries to grab the creature with a parka, but underfoot, the ground forms tentacles which attempt to drag them under.

Petra helps the Doctor trap the troll with her own coat, and the limbs disintegrate.

Two troopers bring Tim Hill into the room Sanders intends to walk to the coast, taking an emergency flare.

They leave the helicopter, and spot a flare in the distance – Sanders, proving that the Spheriosis reaches far away.

The Doctor guesses the way to keep Karl fighting is to put Katy in maximum danger – to take her under the bridge.

She recognises Karl as he sighs, and the entire creature disintegrates – including the tentacles outside.