This is a Dungeon Crawl Classics adventure for Lankhmar for level 2 characters. It uses the DCC ruleset so you will need the core rulebook to run it.
From the publisher:
An unnatural night cloaks Lankhmar in perpetual gloom as unknown killers perform ritual murders on its rooftops!
When a specialist in the employ of the party turns up dead, they must investigate the murder to retrieve what is theirs. Unfortunately for them, doing so leads them into the web of a fiendish plot. Vile sorcery strives to resurrect one of the most feared Mingol warlords in Nehwon’s history!
Can the heroes stop this foul rite before it is too late or will unholy night reign forever in the City of the Black Toga?
Officially licensed from the estate of Fritz Leiber.