This episode was only available via a coded BBC Facebook promotion in September 2016.
Dowcra base. The third Elite Sontaran Assassination Squad closes in on its target. A dozen trained killers, but even they will be unable to bring down the invincible Strang…
Manipulated by the Time Lords, the TARDIS also arrives on Dowcra. And the Doctor is set to encounter the greatest Sontaran ever cloned...