Madquake was the second of two stories comprising the two hundred and sixty-seventh release of Big Finish's monthly range. It was written by Guy Adams and featured Sarah Sutton as Nyssa, Janet Fielding as Tegan Jovanka and George Watkins as Marc.
Abandoned on the planet Callanna, Nyssa, Tegan and Marc take advantage of its therapeutic atmosphere to come to terms with recent events; but others seek to take advantage too. The Slitheen are on their way – and they're ready to sell this world to the highest bidder!
Nyssa and Tegan are stargazing on Callanna when Tegan realises how uncharacteristically relaxed she is, suspecting the planet of affecting her somehow. Nyssa, however, has no such complaints and says to herself that she hopes the Doctor never comes back.
Marc is dwelling on his partial cyber-conversion and wishing that the Cybermen had just killed him when he overhears Nyssa and Tegan arguing, for Nyssa apologises and explains what happened on Deva Loka. Tegan visits Mison and his therapist, Professor Cott, who is trying to isolate the planet's calming effects. Marc accidentally hurts Nyssa when she tries to touch him and lies on a riverbed for two hours in the hopes of finding some peace. Underwater, he senses something approaching.
Marc finishes a run and is told by Professor Cott that he had reached around 100 kilometres per hour. Nyssa and Tegan hear something enter the atmosphere and discuss the Doctor, with Nyssa thinking that the Doctor left them behind because of his guilt and that he would return. Marc discusses him with Professor Cott, who attempts to excuse him by saying that he too was hurting, before suddenly feeling the atmosphere being stolen from the planet.
Nyssa, Tegan and Mison go looking for Marc and Professor Cott as the planet trembles. Professor Cott tells Marc to calm down and that they should stick together because she recognises the approaching ship. Nyssa, Tegan and Mison find them and realise that something is wrong with Professor Cott's voice. She tells them to run as the newcomers are Slitheen, just as she is.
Bella and Grumma approach and Professor Cott identifies herself as Steppa Westma Cotter-Thatch Slitheen, demanding that they leave. They tell her that they are on a human hunt whilst they steal the atmosphere and Steppa holds them back whilst the humans run.
Nyssa, Tegan, Marc and Mison flee. Mison believes that Marc's behaviour has been caused by the planet, which Steppa theorised was sentient. They conclude that the planet has been responding to the wants and needs of the people on it and caused the storms to deal with the atmosphere scoop, which could be killing the planet.
Grumma and Bella give chase, with forty-five minutes left until the scoop is complete. The humans find Steppa, who tells them that she had no part in the continued criminal enterprise of the Slitheen family. They split up, with Marc and Mison acting as bait so that Nyssa, Tegan and Steppa can turn off the scoop. Grumma and Bella take the bait.
Nyssa, Tegan and Steppa get to the Klatch-Par ship whilst the Klatch-Pars gain on Marc and Mison. Marc fights them and holds Grumma hostage to keep Bella from shooting him. Bamma Lotta-Proppa Klatch-Par Slitheen appears and tells the Klatch-Pars that she is ashamed of them and orders them to return home. Once they have left, she reveals herself to be Tegan in Steppa's skin suit.
The Klatch-Par ship takes off and Steppa says that she will remain on Callanna to give the planet therapy. The TARDIS materialises and the Doctor steps out with a face that Steppa says wants forgiveness, but Tegan does not feel that she can. The Doctor says hello and that they all need to talk.
- Nyssa - Sarah Sutton
- Tegan Jovanka - Janet Fielding
- Marc - George Watkins
- Professor Cott - Kate Isitt
- Mison - Raj Ghatak
- Bella - Dona Croll
- Grumma - Harley Viveash
- Robot soldiers - Jacob Dudman
- The Doctor - Peter Davison
- Nyssa wonders if Callanna's relaxing effect is due to positive ions.
- Professor Cott says that she would be more likely to blame Tegan's mother and father for her agitation rather than Tegan herself.
- Nyssa and Tegan have been eating self-heating food packs.
- Marc's heart has been replaced with a CPU.
- Mison says that fighting in a laser battle can give one's self a tan due to the lasers in the air.
- Mison mentions Pavlovian reactions.
- The Slitheen use an atmosphere scoop, which are illegal.
- Bella likens the humans to Parpoxen.
- Cott mentions compression fields.
- Grumma and Bella belong to the Klatch-Par family, ruled by their den mother Bamma Lotta-Proppa Klatch-Par Slitheen.
- Grumma says that humans are less civilised than a Beluvian hen night.
- Grumma asks Bella if she is wearing her gas exchange unit.
- The image of a Slitheen on the cover is a reuse of a promotional image depicting Kist Magg Thek Lutiven-Day Slitheen from Revenge of the Slitheen.
- The following story in this arc, AUDIO: The Lost Resort, was initially going to serve as an instalment of the Monthly Adventures but was later incorporated into the anthology The Lost Resort and Other Stories along with the other previously established release Perils and Nightmares (The Perils of Nellie Bly & Nightmare of the Daleks) in the Fifth Doctor Adventures range.
- Tegan and Nyssa mention their adventure on Deva Loka and Tegan being controlled by the Mara. (TV: Kinda)
- Marc thinks about his conversion. (AUDIO: Warzone, Conversion)