The Unseen Hand

Contains the following stories:
The Mystery of the Free Lances, an original story presenting the "facts" linking the British Lord Trevor to the American Cyril Grisscome, Agent of the Government, and explaining how the Free Lancers of Diplomacy got their start.

That story was followed by 11 adventures, mostly consecutive starting at #73 in the series.
The Aldershot Affair
(Toughing Upon)The Honor of Islam
The Neutrality of Holland, aka The Fight For Holland
The Greater Plot
The Skager-Rack - and Kitchener, aka The Wireless Mystery
The Mysterious Camp in the Pyrenees
A Machiavellian Coup [In Roumania], aka The Roumanian Coup
A Counterstroke in Sweden
The Shifting Ministries [and the Green Circle], aka Outwitting the Green Circle
The Breeding of Suspicion, possibly aka Behind the Secret Panel
Capt. Creighton's Account [of the Russian Revolution], aka The Beginnings of the Revolution