Goran Višnjić – Nikola Tesla
Robert Glenister – Thomas Edison
Anjli Mohindra – Queen Skithra
Haley McGee – Dorothy Skerritt
Paul Kasey – Harold Green
Robin Guiver – Bill Tallow
Erick Hayden – Mr Sorensson
Russell Bentley – Mr Brady
Brian Caspe – Mr Martin
Shaun Mason – Foreman
Directed by Nida Manzoor
Written by Nina Metivier
Script editor: Fiona McAllister
Produced by Nikki Wilson
Executive producer(s) Chris Chibnall, Matt Strevens
Incidental music composer: Segun Akinola
Length: 50 minutes
19 January 2020
At Niagara Falls in 1903, Nikola Tesla is unsuccessful in getting investors for his wireless power transmission system as it is seen as dangerous and crazy. After working late fixing his generator, he comes across a floating orb. Feeling endangered, he makes a run with his assistant, Dorothy Skerritt, as a cloaked figure shoots at them. The Doctor arrives in time to help them escape aboard a train headed to New York City, ditching their pursuer by detaching the car.
In New York, the group finds protesters waiting outside Tesla's lab, having been goaded into fearing Tesla and his inventions by his competitor Thomas Edison. The Doctor identifies the orb as an Orb of Thassa designed to share knowledge, but repurposed for an unknown cause. After spotting a spy for Edison, the Doctor, Graham and Ryan visit Edison's workshop, suspecting him to be behind the attack on Tesla. The cloaked figure arrives at Edison's lab and fatally electrocutes everyone in the workshop before pursuing Edison. The group escapes and traps one of the creatures in a chemical ring of fire, but it escapes by transportation. The Doctor tries to warn Tesla and Yaz back at his lab, but the two are captured and transported to an invisible alien ship above the city. The Queen of the Skithra demands they fix her ship. When Tesla refuses, the Queen threatens to kill Yaz, but the Doctor transports herself onto the ship just in time. She learns that the Skithra ship is just a collection of stolen parts from various species and the Skithra just use others to do their work for them. The Skithra also chose Tesla as their "engineer" because he was able to discover their signal while he had been working on his wireless power system.
The Doctor transports herself, Tesla, and Yaz back to Tesla's Wardenclyffe lab. The Doctor warns the Queen to leave, but the Queen refuses, threatening if Tesla is not given over, she will destroy Earth. While Tesla and the Doctor hook up the TARDIS to help power Tesla's Wardenclyffe Tower, Graham, Ryan, Yaz, Dorothy and Edison ward off the invading scorpion-like Skithra. The Tower activates, and electrical bolts shoot through the Skithra ship, forcing it to leave Earth. Yaz is disappointed to learn from the Doctor that while Tesla was recognised as helping to save Earth, his reputation in the future remained unchanged.