THE DAILY TELEGRAPH says:—
"The discovery of the German Spy system has, we believe, been made in time, and Mr. Le Queux must take his share in the credit of the discovery. His self-sacrificing energy is vindicated to the world. The stories which he tells will come as an alarming revelation to the public."
THE GLOBE says:—
"The audacity of some German agents in England, as revealed by Mr. Le Queux, is only equalled by their enterprise. Mr. Le Queux emphasises the point that it is those rich Germans of the Schulenberg type, for whom some one in our Government or administration seems to have so unwholesome a tenderness, who are the most dangerous. There are many astonishing statements in this most amazing book."
THE PALL MALL GAZETTE says:—
"Mr. Le Queux has devoted special attention to German Spies, and his book will be read with much interest."
THE EVENING STANDARD says:—
"Mr. Le Queux has here written on Spies and spying, as sensational a book as any of his romances. Indeed, it may be questioned whether Mr. Le Queux would have gone the length of introducing into a fictional plot so extraordinary a chapter as that in which he reports one of the Kaiser's speeches."
THE SCOTSMAN says:—
"Mr. Le Queux gives a résumé of espionage methods. He goes over the recent Spy convictions, and describes a considerable number of other cases, unpunished, which have come under his own observation. He has certainly laboured hard to impress the danger of the German system of spying on the mind of the British public, and gives several instances of the ease with which communication with Germany can still be carried out."