The synopsis for Cold Blood, released today by the BBC Press Office.

It is the most important day in the history of Earth: the dawn of a new age of harmony or the start of its final war.

In the latest episode of the time-travelling drama, written by Chris Chibnall, The Doctor must face his most difficult challenge yet. It is a battle in which he cannot take sides and a day when nobody must die…

Cold Blood airs on 29th of May at 6.25pm on BBC One/HD.