Probably my most common complaint when watching the old Doctor Who serials is that they can be too long for the plot they're telling, so could stand to be an episode or two shorter. This is a weird serial in that I think it could probably do with being an episode or two longer.

The first episode sets up the plot. The alien planet of Marinus has a giant machine called the Conscience, which is the arbiter of justice on the planet. It maintained law and order, and was even able to radiate out it's will, eliminating evil thoughts. Then one of the evil alien race known as the Voord was able to resist the machine and corrupted it. Arbitan, the keeper of the machine has reprogrammed it so that it will work on the Voord again, but it requires 5 keys, 4 of which he has misplaced around the planet. So our team have to go out on a number of fetch quests to gather these keys.

The first episode is pretty good. It sets up the plot and the stakes clearly and interestingly enough. I think the Voord look good. It's a simple design, but they look striking and are instantly understood to be villainous just by their apperance. It also sets up a story that requires our heroes to go to a number of different locations and have a collection of mini adventures.

Sounds good, but this is actually also the stories biggest problem. Team TARDIS have to recover 4 keys (5 if you count the fake key they also spend time recovering) from a number of new locations, then conclude the story back at the Conscience by the end. There's only 5 episodes to accomplish all of this. So what tends to happen is that the team arrive somewhere new, we have to then establish the new setting, setup where the key is/might be, setup a threat or obstacle of some sort. Then because there isn't much time the team has to quickly and simply overcome whatever is preventing them from getting the key, so that they can indeed get the key and move onto the next location.

Some of these locations are distinct and interesting. I like the screaming jungle and the ice caverns. The cities are less distinct, feeling more like generic old school Doctor Who sci-fi cities. But there isn't enough time to truly explore any of these locations. So I can't get too attached to any of them. The threats that the team have to overcome, never get to feel that threatening either because the team find out how to overcome most of these threats like 5-10 minutes after encountering them. Nothing can be too hard for our team to get past, because there isn't enough time for them to struggle with the threats.

The best part of the story is the murder plot/court case that takes up much of the last two episodes. This is largely because it's the only plot point that is given any real time. It's also the only obstacle that's preventing the team from getting a key, that isn't (almost) immediately resolved. There's some genuine tension and the team have to actually spend some time solving a number of problems. Even this plotline has some rushed plot resolutions though. Some of the Doctors courtroom antics, and the rescue of Susan both feel too quick and easy in their execution.

Not a bad story by any means. The fact that there's always a new location, new threat, new problem etc... means that this episode is never boring, and it gives the story a fast(ish) pace for '60s Doctor Who. The issue is that because there's always a new location, new threat, new problem etc... we have to rush through many of the plot points in the story. Nothing really lands, it's just a lot of weightless incident.