Jonas Merrick is an agent with MI5.
We are told one huge factor about Merrick when we learn that "In the office ... where he works, they call Jonas Merrick 'the eternal flame'". It isn't a compliment; it's the exact opposite. According to everyone who knows him, "he never goes out. He never goes undercover, never does surveillance, never goes with the teams that kick down the doors or seize the suspects off the street. He commutes into work and sits at his desk and then he goes home." That is apparently on the negative side.
However, more positively is "But he has qualities the hot-shots fail to notice - a steely concentration, a ruthless ability to focus and find the enemy hiding in plain sight". One more good-v-bad comment is "Jonas's colleagues regard him as scratchy, fastidious, old, he is also ruthless, cunning and brutally pragmatic". Those who are closest to him at MI6 "considered [him] a long redundant encyclopaedia of names and faces", redundant because all that information is nicely encoded into the computers so knowing them in one's head is a waste of effort.
Other not very nice opinions of Merrick held by his colleagues, most of whom are far younger than he, include "just so boring and never achieves anything" and "there's a war out there and he's the only passenger in A4 (his division) who doesn't know what the front line looks like or feels like".
None of this comes a surprise to Merrick. When we meet him for the first time, he is ducking out on his own retirement party, at least for a time, "before he was expected for the humiliation and the chuckling, and the insincerity of it". "He had been in A4 for 35 years, a dinosaur. Knew the targets and the addresses that the surveillance people tracked, just did not do the tracking himself, and his stomach bulged and he felt rheumatism in his knees and hips. He took little exercise, only the walk from home to the station, and from the London terminus to Thames House, and the daily reverse."
As derogatory as a lot of the above seems, this is the same Merrick who, while fleeing temporarily his own going-away party at Thames House, encounters a recently converted home-grown Islamic suicide bomber and talks the young lad out of blowing them and others up and removes the explosive vest. All the while reminding himself how his loved wife Vera was honest enough with him to comment, "you're not, never have been, won't ever be, a team player, and you're never in before dawn in crisis time, and you catch the 5.49 back regardless of whether the ceiling is collapsing on the streets of London. You don't give enough back." He does not argue.
And yet ... we will follow Merrick, this "eternal flame", on several very exciting adventures which would surprise those naysayers - and him.