Doctor his technology is inferior and they do not need him. He is cast into a black hole they have created inside Earth that they are using as a gateway to bring in more troops and also to dispose of people they do not need. As he is plummeting into the black hole the Doctor realizes his phone is still connected to the TARDIS and uses it to summon the TARDIS. He finds the Master re-activated and forcefully expels the Shalka from the TARDIS into the black hole. For an unknown reason, the Shalka release Alison back to the surface. As UNIT evacuates the town, a soldier tells the Doctor he has captured one of the Shalka on the surface. The Shalka was accidentally exposed to raw oxygen when a cylinder near it exploded. The raw oxygen caused it to pass out. The Doctor also discovers that Alison is alive, and that none of the survivors from the town have made it to their new destinations. The Doctor attempts to interrogate the Shalka but it recovers and attacks the soldier. The Doctor uses more oxygen to subdue it until he can determine what's going on. He also discovers that the survivors all have sore throats. The survivors and Alison all march against their will to a warehouse in another town. The Doctor arrives in his TARDIS with UNIT men inside and they storm the area. The Doctor removes a living Shalka from Alison's forehead but the effort causes him to pass out. When he recovers they find that all around the world people are mobilizing against their will to strategic points on Earth. The Doctor realizes that the reason everyone has a sore throat is that they all have been emitting subsonic screams when under Shalka control. The Shalka are using the screams to alter the atmosphere of the Earth. As the slaves begin emitting their screams and the ozone layer of the Earth is being stripped away the Doctor takes Alison and the Master back to the Shalka underground lair. When asked if the Master is coming with them, the Doctor tells Alison that the Master cannot leave the TARDIS. The Doctor and Alison confront Prime, who tells them that the Shalka inhabit 80% of the worlds in the universe, living underground off of volcanic energy. When a species is on the edge of ecological destruction, the Shalka come