Prior to being sent to Eireann, the "Cairo Gang" had been stationed for a while in Cairo, Egypt (This was at a time when the British thought they owned most of the planet). During the Great War (W.W.I), Egypt, and especially Cairo, was teeming with smugglers, assassins, revolutionaries, telemarketers and other "undesirables" who weren't very respectful to British interests. Egypt was critical to British control of the region and thus the situation called for experienced and capable agents.
The "Cairo Gang" as they became known was the cream of the British intelligence agencies. They had been handpicked for their skill and it was in Cairo that they established a reputation that rivaled the Royal Canadian Mounted Police for 'getting their man'.
It seems that Michael Collins and his flying columns were producing feelings of consternation in Dublin Castle (the seat of British power in Eireann) which the local agents had been unable to remedy. The local agents had also developed a tendency of being found dead thus more stringest measures were obviously needed. Enter the "Cairo Gang".
The Cairo Gang was suspicious of everyone in Eireann and kept to themselves but Collins had cultivated a spy network of incredible reach. Michael Collins was a master at what he did and it was only a matter of time before he got the lowdown on the Gang. On 21NOV1920 the Cairo Gang went bye-bye.
I intend to buy this book for the history of Eireann, circa 1916-1923, is simply incredible.