Big Finish synopsis;
The year is 2163. Ten years since the Daleks invaded the Earth. One year until the Doctor, in his first incarnation, will help bring the occupation to an end. But for now, their reign of terror goes on.
The TARDIS brings the Doctor and Peri to Scotland – enslaved, like everywhere else on the planet.
When the Doctor falls in with an unlikely group of freedom fighters making that dangerous journey to Orkney, he finds himself trapped – but not only by the Daleks, their robotised henchmen and their human collaborators.
Because history shows that for another year, resistance is useless...
Masters of Earth brings the Doctor dangerously close to changing his own past. In Doctor Who, this is referred to as the Web of Time. Yes, the Doctor can mess about history & future, but he must be very careful not to change his own past. If the Daleks capture him, interrogate him, they will be prepared for his first incarnation's involvement in future. Not to mention, they will learn of the Doctor and perhaps Time Lords decades or even centuries before they should.
Of course, the Doctor's own attitude & character and events plunge the Doctor into the middle of the muddle, anyway. Along the way there are prison breaks, Slythers, Vargaplants, Daleks and Robomen. All the classic 1960s Dalek elements are sharply realized through very experienced use of soundscapes plus the listener's imagination.
Colin Baker really shines in these audio-plays. He gets to work his Doctor they way he never could on television, and by-&-large, he has had far better material to work with. Hearing him battle classic Daleks is a treat.