From the BBC:

It is Christmas Day on a remote human colony, and the Doctor is hiding from Christmas carols and comedy antlers. But when a crashed spaceship calls upon the Doctor for help, he finds himself recruited into River Song's squad and hurled into a fast and frantic chase across the galaxy. King Hydroflax is furious, and his giant robot bodyguard is out of control and coming for them all! Will Nardole survive? And when will River Song work out who the Doctor is?

All will be revealed on a starliner full of galactic super-villains and a destination the Doctor has been avoiding for a very long time.