The Doctor and co. stop by the resort Tranquilty Spa for a relaxing vacation. Or so they think.
However, things (of course) turn out not to be what they seem. Ryan catches a weird parasitic virus, although a non-lethal one, from a snack machine. During his recovery he meets a young woman named Bella.
However, there’s a quick drill due to some form of perimeter breach, and the Doctor discovers a well-armed security room. The Doctor discovers there’s a shield protecting the colony….from….something. Except it’s broken, and something which quickly makes it’s presence known, killing many of the guests. The Doctor manages to repair the shield, but soon the truth comes out. Tranquilty spa is mostly a hologram, surrounded by a barren wasteland and it’s inhabitants, the Dregs. Also, one of the guests, an elderly man named Benni, is outside in the wasteland. The gang try to rescue him in a vehicle, but unfortunately it’s too late for him and the vehicle gets trashed, forcing the gang to get back to the safe part of the resort by using the tunnels.
It’s in the tunnels the truth about why the shield failed is revealed-Bella is the daughter of the resort’s owner, Kane, who Kane left behind to run the spa in hopes of somehow terraforming the planet. So she sabotaged the spa. Bella transport with Ryan back to Spa to finish the job of destroying her mother’s dream.
Another disturbing truth is discovered. Orphan 55 is actually a future Earth, ruined by pollution/radiation, and the Dregs are devolved humans. The big clue is that they’re in a Russian bunker, as well as the race memory of the Dregs the Doctor unearths using her mental powers.
Eventually people make it back to the spa, where the transporter is fixed and the survivors evacuate, except for Bella and Kane who remain behind to fight the Dregs (and are presumably killed). Although the companions are disturbed by this future, the Doctor tells them it’s only a possible timeline.
Next, the group travel to 1903, the height of America’s “gilded age” when new technologies are being harnessed at the turn of the century, leading from the frontier times of the previous century to the more technically advanced and industrialized 20th. Among those in this age are Nikola Tesla and Thomas Edison. Tesla’s ideas are grand but he doesn’t quite have the popular support Edison does. One night at his Niagra falls lab, he comes across a strange glowing orb.
However, somebody’s out to get it, and tries to kill Edison and his assistant. They’re rescued by the Doctor and his companions who head to NYC onboard a train, although they are chased again by the villain, who they barely escape by detaching a car.
The bad guys, disguised as humans are also keeping an eye on Thomas Edison, and kill most of his factory workers. Edison takes refuge with the Doctor and his rival, and the two of course visit the TARDIS.
It’s soon discovered that the aliens, the Scorpion-like Skithra, want Tesla’s help as an engineer for their broken down ship-or else. They recognized Tesla’s wireless transmissions, hence why they needed his help.
Tesla is able to escape, and with his rival Thomas Edison warning people to get off the streets (Blaming the disturbance on Tesla’s “Death ray”) as the space scorpions attack, Tesla and the Doctor fire up his Wardenclyffe tower into a weapon that stuns the alien ship, causing them to leave.
With Earth-and Tesla-safe. The Doctor tells his companions that unfortunately Tesla’s fame would not be realized during his life, although many of his ideas eventually find development in the modern world.
Next: Fugitive of the Judoon….and maybe a big secret at long last revealed.