SPOLIER: the character of John Qualtrough, the spycatcher, is introduced.
This is a cryptic reference to the spycatcher George Smiley, from the novel and TV series Tinker Tailor Solcier Spy.
Qualtrough is a gaelic spelling of the name McWalter.
Phil McWalter was a member of the 1980s band Blanket of Secrecy, whose members used the codenames Tinker, Tailor, Soldier, and Spy to conceal their identities.
McWalter was Spy.