Nightingale Spence is an agent with the B.I.I.
That acronym stands for British International Intelligence, an organization devoted to keeping Britain safe in a very unsafe world. The time frame in which Spence is working is the last couple of years of the 21st Century. 2196 is one date mentioned a few times. The agency, and therefore Spence, has to worry not only activities on this planet but also space stations and colonies on Mars.
Spence is described in the blurbs about these adventures as a "socially non-gendered" operative, codenamed Housekeeping, "a unique blend of assassin, medic, alibi merchant, and therapist to some of the most inventively lethal people in the world". Spence points out on several occasions the codename is especially applicable; Spence's purpose in the BII is to "clean up everyone else's mess". In this regard, Spence likes to differentiate what he does with what the normal operatives for the BII does. Spence is not an operative, per se, as far as Spence is concerned. Spence is the one who is on standby during an operation for when things get 'messy' and the plan has hit a snag, which it often does, and it seems reasonable to ask for housekeeping.
Spence expresses a desire in the first recorded adventure to not be given names of those whose messes are needing cleaning. "It's simpler to remain detached", Spence explains. "I wade through bodies for a living. I don't have time to learn their names." When it is pointed out the person being told this was still among the living, Spence points out "no one starts out dead. They all end up there sooner or later". Spence agrees that this is a depressing attitude to take but also observes that it is the truth.
Spence is likely in his mid-30s when first encountered; this age is based on a thought Spence has about a time twenty years before and being one of a pair of teenagers "playing at being socialites and hating every moment. Where have the years taken that boy to - that lanky youth with so many dreams and so little hesitation?" Spence is nowadays largely a loner. In a later adventure while listening to a colleague talk about his hay fever, Spence "supposed they would be unreasonable to inform the fellow of how little they cared".
The work that Spence does and the messes that are require to be cleaned are almost always 'utterly mad' but despite that, "Spence relished every shred of it"; the job was "a foul but vital occupation within a tangled hush of secrets and deceits".