The automatons execute basic tasks and can respond to certain stimuli. While some are used for very basic (and deadly) security, they are not sophisticated enough for urban police duty. For that, the Yeng rely on human sentries. The Watch have made and kept Mutsai a model of order. They are meticulous, professional, and very well paid.
The diligence of the Watch necessitated creativity on the part of criminals. Mutsai had been built with an underground sewer system rather than the usual canals. Criminals began to use the sewer tunnels for movement, meetings, and hideouts. Gradually they dug tunnels of their own. A network sprang up, crossing and crisscrossing beneath the city.
The underground is not part of the Watch's circuit. The Yeng have tried to renegotiate the contract several times and the Watch always refuse. They will fill in tunnels from above, but they will not go below.
Things grew more complex with the arrival of the nobles. Quarrels between the Houses led to an increased interest in the underground by thieves, spies and assassins. The Houses responded to this security threat in various ways. House Fo planted a moss which gives off hallucinogenic vapors. House Kai released a swarm of razorlings. And House Wen brought a particularly insidious breed of python from the south, which has proceeded to infest the entire system and prove a greater annoyance than the human vermin. To deal with the various threats once and for all, a few have suggested binding ghosts to the sewers to sweep them clean of life. The Yeng are concerned that one of the Houses may actually attempt this, with potentially deadly consequences.
But there are other ghosts in the underground already. When digging the sewers, the Yeng uncovered a complex of ancient tombs. They walled it off, but as the population has increased so has the volume of sewage. It has begun to seep into the once-sealed vaults, causing unrest.
It is rumored that the Yeng are seeking to form a new security force to patrol the underground. Such a group would certainly face danger from predators, criminals, and agents of the various houses, not to mention the restless dead. And it is quite possible that the Watch would view them as rivals. I urge those interested in the position to perform their own research before applying.