The British government has a plan to drastically improveenvironmental conditions, thanks to the Gynt Foundation and its mysteriousbenefactor, 'Mr Hammond'. But the plan is bold and crucially requires theendorsement of a prominent green campaigner to allay any public fears. When the Doctor's former companion Polly sets off toinvestigate a fantastic, new, net zero city, nothing goes quite according toplan. For one thing, the Doctor himself unexpectedly appears. And for another,the city contains a terrible secret. With an older Dodo working for the government, the Doctorand Polly must fight a threat that endangers the whole of humanity.