A slightly interesting take on the concept, although this book narrows down the periods between which travel occurs to 1804 and 1964. I became a little tired of the oft-repeated paradox of killing one's own grandfather, but there is a nice twist at the end that depends on just that. Oddly enough, the world in which the 1960's travelers live is threatened by atomic war instigated by mainland China's desire to invade and regain Taiwan (known as Formosa then); so obviously Leinster was a time traveler himself and visited the 2020's before writing this book.
