What if aliens landed on Earth? No? Well, there is more than one kind of invasion.

This Time Travel Special journeys from H. G. Wells The Time Machine through ideas like The Grandfather Paradox and The Butterfly Effect, to the professional time traveler that is the ever popular Doctor Who. Steven Moffat, David Tennant, Karen Gillan, and Neil Gaiman offer a unique perspective on the Doctor. Furthermore, Edward James Olmos reveals the hidden meaning of the language he created for the vision of the future that is Blade Runner, while Bob Gale and Christopher Lloyd take us behind the scenes of Back to the Future.