This is a novel by George Tomkyns Chesney, starting the genre of invasion literature and an important precursor of science fiction. Written just after the Prussian victory in the Franco-Prussian War, it describes an invasion of Britain by a German-speaking country referred to in oblique terms as the Other Power or The Enemy.
The story is told as a narrative by an unnamed veteran who participated in the Battle of Dorking. He is recounting the final days before and during the invasion of Britain. It is addressed to his grandchildren as an event fifty years earlier. Beginning sometime after an event similar to the Franco-Prussian War, concerns grow with the mobilisation of armed forces near the Netherlands. The Royal Navy is destroyed by a wonder-weapon ("fatal engines"), and an invasion force suddenly lands near Worthing, Sussex.
The story ends with the conquest of Britain; the ransom the victors impose makes the country destitute (special comparison is made to France; likewise humiliated, but able to rise from the blow due to its wealth being in its fields and size, rather than colonies and business). 
This book is a War Fiction, very nicely penned by the author. This book is a reproduction of an important historical work and War Fiction.