The Sea of Death opens with some marvellous model work showing the mysterious location at which the TARDIS has now materialised. The majority of the model for this episode is excellent, with exception being the Voord plunging to his death, which looks very fake to me.

The TARDIS appears to have landed on a warm, sunny beach; but what appears to be quite pleasent soon turns out to be quite nasty - the sea surrounding their location is acid, and they are not alone on the island; strange figures in wetsuits are stalking around the island. Norman Kay's incidental music works well here in creating an unsettling mood.

While the Doctor, Ian and Barbara find a submarine and together deduce a possible senario, Susan has gone explore the mysterious pyramid on the island. The pyramid set is another excellent design from Raymond P Cusick, with the exterior set up to be used to represent different sides, and with trick panels placed into the 'walls'.

Once inside the pyramid, the TARDIS crew come across Arbitan and the device he protecting - the conscience machine. Arbitan fills them in on the history of Marinus, the Voord and the controlling elements of the machine - five 'keys'. Guest star George Couloris is very convincing as Arbitan, a man weho has sent friends, followers and his own daughter on a the quest to recover the keys.

The TARDIS crew eventually decide not to help Arbitan by finding the keys for him; but Arbitan places a force field around the TARDIS, forcing them to help him. They are given travel dials with all the locations pre-programmed; with Barbara being the first to leave. A double cliffhanger occurs as Arbitan gets stabbed by Yartek, and Ian, Susan and the Doctor find Barbara's travel dial with blood all over it...

The Velvet Web sees Ian, Susan and the Doctor finding Barbara being treated like royalty in a room of opulance. That night, as they sleep, devices are placed on their foreheads, but Barbara's falls off. In the morning when they wake, Barbara sees the true nature of Morphoton - a dirty, old ruin. These scenes work quite well, with the audience seeing things from Barbara's perspective.

Barbara escapes, and ends up getting trapped with Sabetha, Arbitan's daughter. She is being punished for Barbara not getting mesmerised by the disk; more importantly, she has the second 'key' around her neck on a chain. The remainder of the TARDIS crew are prepred for their final treatment with the mesmerent; being a shown a room full of old and brtoken items, and believing it to be a fantastically equipped laboratory - a scene well acted by William Hartnell.

Barbara is eventually captured by a fully mesmerised Ian and brought before the true rulers of Morphoton - oversized brains that out-grew their bodies; the props to portray the brains work quite well, pulsating with some eye-stalk movement. Barbara breaks free of Ian and smashes up the equipment in the room - killing the brains and destroying the mesmerent. I wasn't too convinced by this scene - Jacqueline Hill does well to smash up a lot of items, but the death cries of the brains kicks in before she even touches them.

With everyone back to normal, Sabetha and Altos (the man who acted as the TARDIS crew's 'guide' to Morphoton) propose to continue travelling with the TARDIS crew to find the remaining keys - Altos and a friend were sent by Arbitan to find the keys ealier. Rather than travel together, the Doctor goes on ahead to find the final key; where Altos' friend went as well. This gives William Hartnell a well deserved fortnight's break from the series. Susan arrives at the next destination, and is immediately assaulted by loud screaming...

The Screaming Jungle begins with the others arriving to find Susan in shock after being aurally assaulted. As Ian, Sabetha and Altos have a look around to find a clearer way into a ruin, Susan and Barbara share a good character moment, well acted by Carole Ann Ford and Jacqueline Hill. Unfortunately, this exploration of Susan's character is destroyed when she turns into a snivelling wreck after being attacked by a vine; staying this way for the rest of the episode.

Barbara decides to push through the vines and into the courtyard, finding a 'key' on top of statue; as she grabs it the statue revolves, to the horror of Susan and the others who have just returned. The design of the courtyard and statue is another excellent piece of work from Raymond P Cusick, working well to get the best out of Doctor Who's limited budget. Ian decides to stay behind to find Barbara, while Susan, Altos and Sabetha continue onto find the next 'key'. Before Sabetha leaves, she and Ian discover that the 'key' Barbara found is a fake.

Ian travels around with the statue to find another private courtyard, full of booby traps. Barbara ends up getting caught in a net, while Ian gets caught in an alcove. Barbara talks to the man who lives in the building, Darrius, who is looking after the real 'key'. Ian frees himself and he and Barbara help Darrius escape from a plant attack, at the eventual cost of Darrius' life; but before he dies Darrius tells them where he hid the 'key'. Edmund Warwick is excellent as Darrius, a clever scientist whose experiments eventually led to his death, and a very paranoid man, as evidenced by the traps he placed around his home.

With the plants attacking, Ian and Barbara ransack Darrius' laboratory, eventually finding the 'key' in a chemical jar; and discovering the experiment that Darrius carried sped up "the destructive tempo of nature". Ian and Barbara then travel on, arriving in a snowswept landscape... The Screaming Jungle is Ian and Barbara's episode, with both characters carrying the bulk of the action at the expense of other characters, in particular Susan. Jacqueline Hill and William Russell continue to build up Ian and Barbara's relationship, portraying their close friendship well.

Ian and Barbara are rescued from death in The Snows of Terror by fur trader Vasor, but his motives are less than pure, as he forces Ian to trade his travel dial for a fur coat in order to look for the others, and Barbara finds Altos', Sabetha's and Susan's travel dials in a drawer, as well as the other keys. Vasor also attacks Barbara in a very powerful scene that could have led to rape.

Ian finds Altos, tied up and left for the wolves, and they return in time to rescue Barbara and then go and find the girls. Vasor left the girls in a cave with enough material for a small fire, but once that dies they go exploring, and the others catch up with them at a bridge. Vasor abandons them all there, leaving them for what he calls fire demons. Once more Susan is reduced to a snivelling wreck in this episode, pretty much frightened by her own shadow.

The travelers find the next 'key' in a block of ice, surrounded by four soldier-like figures. They work the mechanism to defrost the ice and get the 'key', but awaken the soldiers. Escaping back to Vasor's hut, they have one final altercation with Vasor before he falls victim to the soldiers; and at their next destination Ian gets knocked unconsious and set up as a murderer...

After three reasonably paced episodes, The Keys of Marinus faulters with The Snows of Terror; with the episode feeling very uneven in parts. This can be especially seen with the Ice Soldiers, who serve no real purpose in the episode, except to provide a brief moment of fear and to dispatch the villain of the episode in a quick manner.

Ian awakens and finds himself under interrogation at the start of Sentence of Death. It seems that in the city of Millennius has a justice policy of "guilty until proven innocent"; with the burden of proof placed on the accused to clear their name. The others are allowed to visit Ian in prison, which is when the Doctor re-appears on the scene.

It's good to see William Hartnell again, and the Doctor is in his element once more as he takes on the job of defending Ian. As well as sending everyone off on their tasks, the Doctor does his own work; interview Tarron, Ian's interrogator. It seems that Ian has been accused of murdering Eprim, and as only Ian and Eprim had planned to steal the final 'key', Eprim must have told others about it ad got murdered for his troubles. The set design of the trial room is very ornate, with the symbols on the wall reflected in the costuming with the symbols on the collars of male outfits.

It seems that the relief guard Aydan was involved in the crime, with Susan and Barbara's questioning of him pushing the man too far. It appears that Prosecutor Eyesen is also part of this conspiracy. The Doctor throws some subterfuge into his defense case, causing Aydan to crack, but before he can reveal who else was in on the conspiracy; he is murdered. Despite this; Ian is still found guilty, and Susan is abducted by the remaining conspirators...