Warehouse of Woe
Side quest
Novigrad suggested level 13 
On the world map
From the journal
Geralt can hardly spend a day in even the most seemingly idyllic village without being asked to kill a monster, so it should come as no surprise such requests came to him in Novigrad as well. On one occasion he was asked to clean a warehouse of nekkers. The two owners - a man and a dwarf - blamed each other for attracting the monsters there in a plot to gain sole control over the building.
After examining all the evidence, Geralt decided the dwarf was at fault.
After examining all the evidence, Geralt decided the man was at fault.
Geralt found out that someone had ensured the nekker could break out of its cage.
Geralt didn't care much for squabbles between merchants. He didn't bother to collect evidence and in the end never found out who truly was to blame for freeing the nekker.