Deep time

" The Phaeron disappeared from the universe over a million years ago. They travelled among the stars using roads made from time and space, but left only relics behind. But what actually happened to the Phaeron? Some believe they were eradicated by a superior force... Others claim they destroyed themselves. Or were they in fact the victims of aneven more hideous fate? In the far future, humans discover the location of the last Phaeron road - and the Doctor and Clara join the mission to see where the road leads"--Amazon.com.