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The Isos Network was the fourth and final story of the second series of The Early Adventures, produced by Big Finish Productions. It was written by Nicholas Briggs, narrated by Frazer Hines and Wendy Padbury and featured the Second Doctor, Jamie McCrimmon and Zoe Heriot.

Publisher's summary[]

The Doctor, Jamie and Zoe are leaving Earth after having successfully defeated a Cyberman invasion... The Cyber-fleet is still exploding... But something is escaping through the mass of vaporising debris.

In hot pursuit, the Doctor and his friends find themselves drawn to a mysterious planet where strange beasts slither through the streets of a deserted city... And an old enemy lurks beneath the streets.

As a force of heavily-armed aliens arrives, a battle to save the entire galaxy from invasion begins.


Part one[]

The Second Doctor, Jamie and Zoe are leaving Earth in the TARDIS after thwarting the previous Cyberman invasion, when they discover one Cyber-ship escaping and attempt to follow it. However, the TARDIS is damaged in the pursuit and they land on the planet Isos II and decide to go exploring for the ship since the TARDIS needs to re-calibrate. They discover a large seemingly-abandoned city and accidentally step in some slime, then decide to move inside the city and figure out what's going on when they realise no one is around and there's lots of slimy trail. They are surrounded by slug creatures who at first appear to want to hurt them but turn out to be friendly and play with the three. The three are eventually lead to a deserted underground monorail station and Zoe gets trapped in a lift where she is plummeted below.

Meanwhile an Isos ship, named the Braxos, lands on Isos and dispatches a crew to discover the source of an energy spike they picked up and end up finding the TARDIS, the source of the spike. They have been sent to discover what had happened to a colony on Isos II that disappeared. Jamie, while searching for Zoe, ends up falling down a broken escalator while the Doctor is discovered by the dispatched Isos security team. Zoe begins to explore the tunnels but she hears steps behind her and tries to outrun them. The Doctor is brought back to the Isos ship to talk with Commander Seru who demands he explain why the population of the planet they're on, Isos II, has disappeared to which the Doctor doesn't have an answer but a vague suspicion. Jamie stumbles on cyber-pods and the Cybership they were pursuing earlier and realises that the Cybermen have already arrived on the planet. Zoe follows a slime trail, wondering how the slug creatures could have penetrated this deep, only to be cornered by some Cybermen....

Part two[]

The Doctor shows the Braxos crew that the energy signatures they detected were not his TARDIS but something else. Zoe is saved by a creature, an Ison named Hilsee, and Jamie stumbles on the Cybermen. Seru interrogates the Doctor further to find out why he has come to Isos II. Hilsee explains to Zoe what happened to Isos II after the arrival of the Cybermen and she discovers that he has already been partially converted before he escaped. The Doctor explains to Seru that he deduces the Cybermen arrived and converted the inhabitants of Isos II. They use the ship's built-in navigations and maps, they manage to locate Zoe and Jamie. Jamie watches as one of the slug creatures they played with earlier confront and get killed by a Cyberman. The Doctor, Seru and a security squad penetrate the depths of Isos II, heading into the tunnels of the monorail track, while the Doctor warns Seru to request back-up from her home planet, but she refuses, confident in the team she has chosen. The Cybermen observe them from the shadows and prepare their counter-measures. Hilsee takes Zoe to the chamber containing the cyber-pods and shows where he was converted, and explains everything that happened to him to Zoe, how he lost his friends and family as they were murdered in the conversion process and so forth.

The Cybermen, in a separate chamber, discuss a plan to increase power in order to awaken the Cyber-controller (the same as the one found in the tombs). Jamie finds a shaft similar to the one Zoe fell down earlier and attempts to scale it but he is discovered by masked men...

Part three[]

The masked men are revealed to be part of the Braxos security team lead by Captain Enab that had been dispatched earlier. Meanwhile, Zoe explains to Hilsee that they must find the Doctor and explain what's happening and Hilsee reluctantly agrees to help. Jamie is reunited with the Doctor and reveals what he found out and they make a plan but the slime from the slug-creatures all over the junction box catches the Doctor's attention and he proceeds to investigate. Zoe and Hilsee accidentally destroy some of the slug's eggs while also investigating the slime all over the junction box and make a break for it when the slugs become angry with them. The Doctor deduces that the slugs have been using the slime to cut the power by having it short-circuit the boxes. However, they see they are being watched by the Cybermen through a surveillance camera and destroy it and immediately make a plan. The slugs carry Zoe and Hilsee off and Zoe hesitantly assures him that the slug creatures seem nice and wouldn't want to hurt them and guesses that they're being taken to the surface. The Cybermen and Cyber-leader revive the Cyber-controller and bring them up to date on the situation. Jamie and the Doctor, Seru, Enab and the squad are found by the previously dispatched Cybermen and they kill a squad member. They attempt to escape the Cybermen but half the squad is killed in the ensuing bout. The Doctor instructs them to try something that works at first but then fails, however, they are saved by the slug creatures who have brought Zoe and Hilsee along.

The Doctor conjectures that the slugs are can at least sense feelings and responded to Zoe's emotional need for help. In the meantime, Jamie hears something along the monorail track and it turns out the Cybermen have activated a travel pod to head to the Doctor and company's current position and run them over. The eggs on the monorail line begin to hatch but they see the pod headed towards them, its light getting brighter...

Part four[]

The liquid from the cocoon drips onto the power junction and short-circuits it, deactivating and stopping the travel pod. The Doctor notes that this pod is different to the ones they saw on the surface. The Cybermen prepare another plan of attack after the Cyber-controller accesses the repository of cyber-experiences and identifies their enemy as the Doctor. The Doctor, Jamie, Zoe and Hilsee go inside the travel pod but before they can get out, the pod shuts and they get stuck inside and the pod begins to move, bringing themt o the controller. Hilsee realises that he is being controlled by the Cyber-controller and the Doctor deduces who they are being brought to... but they also realise the pod is capable of traveling through hyper-spatial gateways and that its next destination is Earth. The Doctor and company are brought before the Cyber-controller and Hilsee, now under the control of the Cyber-controller, escorts Jamie and Zoe to be converted. Meanwhile, Seru attempts to call for help. The Cyber-controller intercepts Seru's call but reveals it wants Seru to summon back-up, much to the Doctor's confusion. Just then, they are distracted by a blinding light. While they are distracted, the Doctor slips into the travel pod as the Cyber-controller prepares to activate the conversion process on Jamie and Zoe, but the Doctor's actions do not escape its notice and it sends Hilsee to go deal with him.

Hilsee confronts the Doctor but the Doctor manages to help him struggle and break free of the Cyber-controller's grasp, while Jamie manages to escape the conversion bed and helps Zoe. The controller sees this and brings Hilsee, back under his control and orders him to capture them but Hilsee begins to struggle again and Jamie, Zoe, and the Doctor in the moment of distraction, escape, with Jamie and Zoe heading into the tunnels on the Doctor's instruction while the Doctor goes back into the pod. Hilsee helps the Doctor as he programs the pod to explode and destroy the entire underground network. However, the pod cannot be detonated automatically and must be piloted and the Doctor initially prepares to sacrifice himself, however, Hilsee, much to the Doctor's protests, volunteers himself instead, claiming he is already dead having been partially cyber-converted. Just then the Cyber-controller confronts Hilsee and they fight, while Hilsee helps the Doctor escape and seals himself and the controller in the pod and it rockets away. Initially distraught, thinking they are trapped underground with the explosion imminent, the three are found by the slugs and despite Zoe's protests to save Hilsee, they manage to escape the tunnels with the slug's help in time before the pod detonates, with Hilsee successfully declaring his victory just as it explodes.

The slugs bring the three to the TARDIS just as the tunnels explode and cause the city to collapse, seemingly destroying the Cybermen once and for all. The three mourn Hilsee but are then found by Captain Seru's reinforcements, however, they slip away in time. Jamie asks the Doctor if that truly is the end of the Cybermen but the Doctor reluctantly explains that since the Cybermen base their lives around survival, the three may likely encounter them again, however the events of today have certainly been a major set-back for the Cybermen. They then dematerialise in the TARDIS.



  • The Doctor claims he is from Earth.
  • The Braxos security team, when they find Jamie, refer to his kilt as a "skirt".
  • The monorail system in the city was replaced by air cars years ago.
  • Cybermen can transfer data quickly between each other by transferring the data via electrical impulse between their heads.
  • The travel pod is designed to plot courses through hyper-spatial gateways. Zoe explains that they are a theoretical way of traveling vast distances across space.
  • Zoe compares the travel pod and the tunnel system to a particle collider.
  • The Doctor explains the Cybermen are using centrifugal energy to create a space-warp.
  • Warp bubbles have no beginning and end.


  • This story was recorded on 19-20 November 2014 at The Moat Studios.
  • The events of this story were teased in Last of the Cybermen, which was released only months earlier.
  • The sonic screwdriver is used, in keeping with the show's continuity when the sonic screwdriver only appeared at the end of Season 5's TV: Fury from the Deep and not appearing anytime before.
  • The Doctor claims he is from "Earth", in keeping with the show's continuity of the time before the end of the Second Doctor's run when his true race as a Time Lord was revealed in the final serial TV: The War Games, but before then was still unknown.


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