The first of these, "The Case of the Russian Bear," involves the British Government, as represented by Mycroft Holmes.
We are not told any more about Abrahams in the Canon, but he may be identified as Sir David Abrahams, who makes his appearance in "The Enfield Rope." I.
The circumstances surrounding it are mentioned in "The Disappearance of Lady Frances Carfax," where Holmes mentions to Watson that it would be impossible for him to leave London while "old Abrahams" is in such danger.
The first of these, "The Case of the Russian Bear," involves the British Government, as represented by Mycroft Holmes