Reviewed on 9/26/2018...
Four part episode aired in 1972. I've watched this one over ten times at least, the first time being on my B/W TV as an 11 year old. The time paradox element at the heart of the plot is an intriguing one which is delivered well onscreen, and was one of the show's first stabs at the complexities of time travel, introducing the Blinovitch Limitation Effect. It's quite similar to the Outer Limits episodes "Soldier" and "Demon with a Glass Hand" which involve future soldiers travelling to the present to alter history.
Aubrey Woods as the Controller steals every scene he's in. Like many Doctor Who actors through the years, many are thespians from the Royal Shakespeare Company, and were quite often prone to treating the studio like the stage. The Doctor drinks alcohol, some wine, in this episode too (along with a slab of gorgonzola) which is almost unheard of in the series; however here it accompanies the 3rd Doctor's dandy nature well. The Doctor also outright shoots somebody dead here. I think most fans just look the other way from this fact, as some sort of mistake (which it probably was, the director being rather unfamiliar with the show.)
The Beeb has been adding in CGI effects to many of these older episodes of late and this is one of them. They fit in seamlessly here and really enhance the viewing. The Dalek voices have also been updated by the current showrunner Nicholas Briggs, as the original voices were rather disappointing.