The Doctor and Molly find themselves at the very edge of creation. But something dangerous seems to be heading back into the known universe from the very end of time.

The crew of the cryo-ship Orpheus, including its medical officer Liv Chenka, have their mission parameters to adhere to; but the arrival of the Doctor and Molly changes everything. An ancient and terrible force is on a collision course with them all and the outcome seems to be a matter of divine destiny.