Time drives every heartbeat, every geological layer, and the expansion of the universe itself, and physicist Michio Kaku spends four episodes tracing it at each of those scales. The opening episode, Daytime, asks whether the sense of time passing comes from inside the mind or from the world outside, using sleep studies and simple perception experiments to test both answers. A second episode follows the biological clocks that govern hormones and sleep cycles, showing how the body stays synchronized to a 24-hour rhythm even in isolation. A third takes Kaku to some of the planet's most exposed geological sites, reading millions of years of history directly out of rock layers. The final episode turns to cosmology, where Kaku lays out the physics of time dilation and the search for a beginning, and possibly an end, to time itself using the tools of string theory. Kaku narrates throughout, moving from a subjective, felt experience of time to the hardest physics of when and how it started.