Terry Nation manages to do what many thought impossible - write a story that both feels rushed and like it's being dragged out at the same time.

He's managed to craft this by attempting to use the serial-within-a-series style of Classic Who to tell different stories across one single serial, something that... Well, it's not a bad idea. In fact, two future serials by different writers would contain different stories and be quite successful, these being The Key to Time, which of course was based on this story, and The Trial of a Time Lord. Well, up to episode 14, but that's a story for another review.

Nation would also repurpose the idea for The Chase and The Dalek's Master Plan, both of which I will also review, and both of which suffer from a similar issue to this story.

Too many locations.

Unlike The Key to Time, which has 26 parts, broken down into five four- and one six-part sub-serials, or Trial of a Time Lord, 4 parts in three four- and one two-part sub-serials, Marinus has six parts to tell five stories. Now, there's not actually much story going on in each location.

Arbitan's lair and the first key take up one episode, and the story here boils down to 'Arrive, explore, oh no! Acid lake, get trapped, gain Arbitan's trust, refuse to find remaining keys, return to TARDIS, oh no! Forcefield, return to Arbitan, leave to find keys, oh no! Arbitan's dead'. Five of these are completely useless, especially given as they can alter the destination along the path the bracelets are set for, and Arbitan must have released the TARDIS immediately. The fifth one, 'Arbitan's dead', is pointless because a later plot point is 'Oh no! Arbitan's dead'. Now, some would say that obviously it needed to be repeated five weeks after it happened because audiences might not remember. I would argue that it didn't need to happen here.

Why am I diving into this episode? Because aside from the final two, it's the best paced, in part because this key isn't one that needs to be found. There are one too many keys in this story, and the Cling Film Ice Caves (hey, that's a compliment, it's amazing that they managed to build ice caves on a low budget, and visually they work great! Audibly, however...) have a key that's superfluous to the story.

There should be four keys, one with Arbitan, one in the city with his daughter and her boyfriend, who haven't gone on because they were mind controlled by some brains in jars. One in the jungle (or the ice caves, I prefer the ice caves) with a decoy key, and then one that Altos's friend was going to steal and where Ian is framed for murder. Then the middle two stories would have the time to be properly fleshed out with ideas from whichever is dropped (screaming jungle, please) used to give more substance to the plots in each remaining location.

Now, that tackles the rushed-ness. Onto the dragging.

What the characters have to do in each setting does not fill 25 minutes, and the remaining time is padded out. It's not the most obvious padding in Doctor Who history (hello, Four and Romana walking around Paris, hello, two minutes of beach before The Leisure hive starts, hello, The Mind Robber Part 1), but it's there. Unfortunately, this means that some scenes drag on just a little too long, resulting in really weird pacing.

Ultimately, it's a good idea, with poor execution.