The government of Horizon is a human institution; it is not some flawless Star-inspired hierarchy where corruption is impossible and the rules are sharp and clear, but nor is it a Fire-formed anarchy ruled by brute force and mad whimsy. Bribery, nepotism, and dirty tricks can go a very long way, but the Mayor's office and its ministries have their own way of looking at things and their own agenda; whilst low-level officials can be bribed to do almost anything, their power to do real damage to the Mayoralty's agenda is limited, and powerful individuals aren't easily tricked into screwing themselves over.
Horizon has always enjoyed a strange sort of independence, even during the height of the Empire. The Emperor always had a fondness for the city of his birth which made him reluctant to intervene in its affairs with too much of a heavy hand; by and large he allowed the Mayors to conduct the business of the City as they pleased, overruling them only when gross mismanagement was apparent.
The Emperor is regarded as the first Mayor of Horizon, being the leader of the human tribe occupying the City when he killed the God of Oaths and ended the dreamtime. There are still one or two governmental traditions date back to this time.
The aftermath of the war has left Horizon's masters in an interesting dilemma. On one hand, the four victors have established powerful embassies within the City from which their spies operate, and if Horizon seems to be getting too powerful the victors may unite once more to smack it down again. On the other hand, the Mayor's office may now operate entirely independently of the Emperor; if they can just avoid a revolution and keep the Four Nations at each other's throats, the rulers of Horizon will reap the rewards of the City's postwar recovery, and indeed could find themselves the rulers of a new Horizon Empire should things go exceptionally well for the City.
The current Mayor is Colonel Andrew Zero, a gruff military veteran of 56 who has retained his position for some 30 years, thanks mainly to his pragmatism, ruthlessness, and political skill; if you took a stereotypical retired English major's mannerisms and personality and gave him the Machiavellian cunning and worldview of Ankh-Morpork's Patrician you'd end up with a fair idea of what Mayor Zero is like. Mayor Zero ended a succession of weak Mayors, most of whom were puppets of one Nation or another and were rapidly assassinated by rival Nations: his election is widely regarded as the point when Horizon stood up, brushed itself off, and started working its way back to being a world power again.
In general the current agenda of the Mayoralty is as follows:
NOTE WELL: The Mayoralty is not a claustrophobic, Orwellian government with an ultra-efficient police state at its beck and call. The Imperial government was like that, but that has been utterly dismantled. The Mayoralty is an institution with various departments and ministries which originally dealt only with the local issues and troubles of Horizon; now that the Empire is gone it has had to adjust to the new world order, and has only really managed to do so thanks to Colonel Zero's reforms. Imagine what would happen if Parliament were dissolved and the Greater London Assembly were the highest power in the land...
Two types of organisations exist within the Mayoralty:
Bloated ministries/councils/whatever, staffed by bored paper-shufflers who supplement their meagre income with lots and lots of bribes. Everybody knows the names of the major ministries, which exist mainly to a) sort through the...
Small, sometimes frighteningly competant cliques, subdivisions, sub-sub-subdepartments and so forth existing within the ministries. You probably wouldn't know much about these shadowy sorts unless you were either a) in one or b) ran across evidence of their work. The situation is complicated because these damnable cells never use their full name: they're always (for example) "the Service" instead of the Military Diplomatic Service. These are the people who get the sensitive work done; members of these groups tend to be fairly devoted to their group's agenda, and most of the groups are fairly devoted to the Mayoral agenda (although friction happens frequently - even when cells *don't* go rogue). It's a hateful thing for a low-ranking ministry bureaucrat when one of these flash operators bursts into their office, demands their co-operation, wave around licences allowing them to cut through the bureaucracy like a hot knife through butter and generally forcing them to be efficient.
Members of these groups tend to be fully aware of the other little subdepartments within their own ministry, and dimly aware of the functions of subdepartments in other ministries.