If you were to randomly travel in time and space, where would you end up? Well, if our own battle-torn history was anything to go by, you'd like as not end up in a time and place of war. The thing is, however, the Doctor is not, for once, travelling randomly – he's been charged with carrying out errands for the Time Lords. And the most tricky of those is to go the planet Skaro, deeply enmeshed in a thousand year war, and put paid to one of the most heinous plans that could risk the universe – that of Davros to create his Dalek race.