Shirna and Vorg with the Miniscope

The TARDIS materialises in the hold of a cargo ship on the Indian Ocean. The Doctor though is puzzled as he was heading for Metebelis 3, a famous blue planet in the Acteon galaxy. The Doctor and his travelling companion Jo Grant start to explore the ship but are forced to hide when a Major Daly, his daughter Clare and Lieutenant John Andrews, a seaman, enter the saloon. Clare and Lieutenant Andrews then leave to take a walk around the deck while Major Daly falls asleep. Jo picks up, from a table, a copy of the Illustrated London News and discovers that it is dated 3 April 1926. Suddenly a plesiosaur rises from the sea. In the confusion, The Doctor and Jo try to leave but are seen by Major Daly. Accused of being stowaways they are locked up in a cabin. There, The Doctor discovers that the ship is the SS Bernice and the date is the 4 June 1926 - the day that, according to history, the ship vanished just two days out of Bombay. Jo then notices that when they entered the cabin the clock read 7:35 and now it reads 6:40 and it is also daylight outside when it should be night. Just outside the cabin door they also spotted a hexagonal metallic hatch in the floor, that no one else can see, and, having used Jo's skeleton keys to escape from the cabin, Jo and The Doctor examine it.

Meanwhile on the planet Inter Minor two Lurman visitors arrive in a cargo shuttle. They have with them a machine called a Miniscope. Having spent all their available credit bars on the trip to Inter Minor they request the Minorians to allow them to stay using a stolen visa application. As the Minorians decide what to do Vorg checks the Miniscope is undamaged and starts to make it ready for their next show.

After examining the hatch on the floor The Doctor deduces that it is secured by anti-magnetic cohesion and that he needs a magnetic core extractor to open it. He has one in the TARDIS and so he and Jo head for the saloon. There, they see Major Daly and the others going through exactly the same sequence of events as before. They manage to return to the hold unseen but as The Doctor exits from the TARDIS, having fetched the piece of equipment he requires, a giant hand suddenly emerges from the ceiling and removes the TARDIS from the hold.

Orum and Kalik

The hand belongs to Vorg who has found the TARDIS in Circuit Three. He replaces it inside the Miniscope's field as two of the Minorians, Kalik and Orum, enquire as to what the Miniscope actually does. Vorg explains that it contains miniaturised life forms from across the galaxy, including Tellurians, a Cyberman, an Ogron and Drashigs. To demonstrate that the pictures shown on the screen are not recordings, Vorg turns up an Aggrometer which according to Vorg will make the specimens behave more aggressively. This though has an alarming affect aboard the ship. The Doctor and Jo have again been spotted by Major Daly, but this time Lieutenant Andrews challenges The Doctor to a fight which The Doctor wins. But as he and Jo hurry to the hatch they are chased by armed sailors. Jo starts to unseal it but Lieutenant Andrews and the sailors arrive. Vorg turns the Aggrometer off and Lieutenant Andrews and the rest of the crew return to their duties without a second glance at The Doctor and Jo. Opening the hatch, The Doctor and Jo descend and find themselves inside the workings of a giant machine.

On learning the truth about the Miniscope a Minorian called Pletrac orders that the machine must be destroyed as it contains livestock. An eradicator then arrives but when it is used on the Miniscope it fails to have any affect. Vorg then checks that no damage has occurred to its contents. It is then Vorg sees The Doctor and Jo inside the machine. Orum spots and then removes the TARDIS from the Miniscope. However, no longer influenced by the Miniscope it suddenly grows to its normal size.

Claire and Andrews onboard the SS Bernice

Trying to find a way out, The Doctor cuts through a restraining bar over another hatch. On going through it The Doctor and Jo find themselves in a cave. But they soon discover that outside the cave entrance is a marsh inhabited by large ravening caterpillar-like Drashigs start to hunt The Doctor and Jo. Watched by the Lurmans Shirna gets Vorg to distract the creatures allowing The Doctor and Jo to return to the cave and so back inside the workings of the machine. However, the Drashigs - which hunt by smell – follow them. The Doctor realises that they are inside a Miniscope and tells Jo that he had been instrumental in getting the High Council of Time Lords to ban them. But it looks as if at least one of them survived.

As the Drashigs roam through the machine's innards, The Doctor and Jo return to the ship to get some rope with which The Doctor plans to reach the base of the Miniscope in the hoping of finding a way out. A Drashig though smashes through into the ship but is killed by Major Daly with a machine gun. Lieutenant Andrews then throws some dynamite into the machine to try and kill another Drashig. He succeeds in killing it but his actions cause a general power failure in the Miniscope.

While Jo is held on the ship, The Doctor manages to escape from the Miniscope. Like the TARDIS as soon as he is outside the influence of the Miniscope he grows to his full size. Alarmed at The Doctor’s sudden appearance Pletrac tries to use the eradicator to kill The Doctor. Luckily for The Doctor Kalik has seen an opportunity to to gain power for himself and has disabled the eradicator so as to prevent Pletrac from using it. The Doctor then takes control of the situation. His priority is to rescue Jo and return the rest of the occupants to where they originated. But a plate at the base of the Miniscope is moving as the Drashigs, who have followed The Doctor, try to break out. The Doctor links the Miniscope to his TARDIS so that he can then re-program it. He builds a device to achieve this and instructs Vorg on how to use it. He then transports himself back into the Miniscope so that he can rescue Jo.

The Doctor with his Sonic Screwdriver

While he is gone, Pletrac damages The Doctor’s device, leaving Vorg to try and repair it. It is then that Vorg discovers that a component from the eradicator has been hidden in one of his bags. He wonders how it came to be there. It seems that the component from the eradicator has been placed in Vorg's luggage so that the Lurman will be blamed for the failure of the eradicator. But Vorg has greater concerns when the Miniscope’s power runs down and the life support systems start to fail.

Kalik then releases the Drashigs from the Miniscope which causes them to grow in size. After Kalik becomes their first victim Vorg fits the missing component to the eradicator and destroys the Drashigs before they can kill anyone else. He then operates The Doctor’s device that he has managed to repair. This though causes the Miniscope to blow up. But not before the life forms are retuned to their natural habitats and The Doctor and Jo return to Inter Minor. With the Miniscope out of action for good, and with Vorg finding another way of earning some credit bars, The Doctor and Jo leave in the TARDIS.