Attempting to bring Graham, Ryan, and Yaz back to 21st century Sheffeld, the TARDIS instead arrives in Montgomery Alabama, at the beginning of a pivotal moment in civil rights history. The day Rosa Parks refused to give up her seat on a bus. Although pleased to meet her, the Doctor has evidence that somebody is trying to interfere with the pivotal event, judging by the Atron (Time Travel) energy in the area.
She’s right. The group eventually encounters a man named Krasko, who is from the same basic time as Captain Jack and River Song, where humans have developed cheap time travel devices called vortex manipulators (He’s also a criminal from River’s own prison, Stormcage). He wants to change this moment in history.
The group are able to eventually stop him with his own vortex manipulator, and also stick around with Rosa to make sure events go the same way.
The group then returns to Sheffeld, presumably so the companions can return to their normal lives. Yaz also invites the Doctor and Graham to meet her family, but all is not well. Yaz’s neighbor has been killed by a giant spider, and one showed up at Graham’s house as well. They team up with a local scientist-a colleague of the dead neighbor-who discovers there’s weird spider activity going on in Sheffeld.
It all centers on a new hotel, one that Yaz’s mother used to work at, and one run by Real estate tycoon Mr. Robertson (Played by Chris Noth of Law & Order and Sex and The City fame). Turns out, the Spiders have mutated due to giant size due to a mix of toxic waste and genetic experimentation.
Eventually the Doctor and group are able to lure the Spiders to a panic room by playing dubstep .
….except for the mother Spider, which is having respiratory problems due to getting too big. Robertson decides to just kill the thing with his gun, something that really angers the Doctor.
Eventually, although they are now free to return to their own lives, the group decide that they want to travel with the Doctor instead. Cue the hands!