By day Nicco is a city guardsman valued as much for his agility and strength as his astounding ability to solve crimes. By night he works for La Mace dâ€™Ars (mafia-like organisation) paying off an old debt, as their chief assassin. He doesn’t relish his second lifestyle, but does it out of fear of his powerful mafia creditors. When one of his missions goes badly wrong and he mistakenly kills an innocent family this double life backfires on him and he is asked to solve his own crime.
The innocent family in question is that of Franco di Minisco, a very influential merchant in the cityâ€™s upper echelons. He makes it clear to the special investigation branch of the city guard (the PCs) that he will not be satisfied until the killer is found. He has so much sway that he could easily get them sacked (or even hung, if itâ€™s a particularly sadistic campaign world) for inefficiency if they failed to solve the crime.
The other city guards (PCs) suspect nothing and he must lead them off his trail while the GM places tantalising clues pointing to his guilt. Even when the other PCs find out, will they really grass him up, will they be forced to arrest someone they know to be innocent, or will they simply admit defeat and risk losing their jobs?
There are many ways out of this situation, foremost being to find someone with a grudge against Franco di Minisco and get them to murder him (Iâ€™m not saying these ways are morally scrupulous, just possible). Or the PCs could elope from the city, which would have the unfortunate consequence of making them look guilty.