At the end of the 1968 serial The Invasion, the Second Doctor and his companions defeated a fleet of Cybermen attempting to invade Earth. But did they? As it turns out, one Cyber-ship escaped. The Isos Network, the latest in the series of Second Doctor audio adventures from Big Finish, sees the Doctor, Jamie and Zoe pursue this ship to the planet of Isos 2, where they find a deserted city, giant slugs, and the Cybermen rebuilding their power.

The link back to The Invasion will please fans of the era, and writer/director Nicholas Briggs does a lot to recreate the classic ‘60s style, with monsters skulking about in underground tunnels, jumping out when it’s time for the cliffhanger, and with a reappearance from the original Cyber-Controller.

However, the adherence to the format of Troughton-era Who isn’t entirely a good thing in this audio’s case; the story takes a long time to get going, with the first episode (of four) largely consisting of our heroes exploring corridors – an old Who cliché, and one that particularly drags in the audio format. The plotting feels generic and predictable, with certain plot points trying so hard to mimic classic adventures that they end up over-familiar, and it’s only in the final episode that the confrontation between Doctor and Cybermen really gets going.

Despite these story issues, the production is of as high a quality as ever. Original Jamie and Zoe actors Frazer Hines and Wendy Padbury both play their characters and narrate the action, plus Hines puts in a very respectable Patrick Troughton impression; he may not be the man himself but he gets all the mannerisms right, and when the Doctor and Jamie interact, you can easily forget that they’re played by the same actor. It almost feels like this fan favourite TARDIS team are properly back together again, and their interaction offers a lot of fun, particularly the recurring joke in which Jamie defends his wearing of a kilt. Credit must also go to Kieran Hodgson, who puts in a memorably tragic performance as Hilsee, a resident of Isos 2 who’s ended up on the wrong side of a cyber-conversion unit.

With this much loved trio along with the classic Cybermen in a sequel to a fan favourite story, there’ll be enough in The Isos Network to please any devout fan of the Troughton era for two hours. But the story’s failure to do anything that feels particularly new or imaginative, as indeed Troughton’s serials felt at the time, means it’ll struggle to win over the unconverted. 

DOCTOR WHO EARLY ADVENTURES 2.4: THE ISOS NETWORK / AUTHOR & DIRECTOR: NICHOLAS BRIGGS / STARRING: FRAZER HINES, WENDY PADBURY / RELEASE DATE: OUT NOW