What connects a missing astronaut, birds behaving strangely in Peru and a US naval officer who washes up on a Madagascar beach? The Doctor, Yaz, Ryan and Graham split up to investigate these mysterious events across 21st-century planet Earth, but as the mystery deepens and lives are put at risk, they face a deadly race against time to save humanity. Guest starring Warren Brown and Matthew McNulty, with Jodie Whittaker, Bradley Walsh, Tosin Cole and Mandip Gill.