1903. On the edge of Niagara Falls, something is wrong at Nikola Tesla’s generator plant. Who or what is sabotaging the maverick inventor’s work? Has he really received a message from Mars? And where does his great rival Thomas Edison fit into these events? The Doctor, Yaz, Ryan and Graham must join forces with one of history’s great minds to save both him and planet Earth.

Ko Sho Blo! Trigger-happy space police the Judoon are targeting 21st-century Gloucester. The Doctor, Yaz, Ryan and Graham race back to Earth in order to prevent them doing too much damage to the cathedral city. But who are they looking for, and what did they do to incur the wrath of the Judoon?