Warhammer Fantasy Roleplay (1st ed, 1986), p307 — The Asylum

As Oldenhaller told the characters, the gem was in the possession of Kurt Holger, chief of the Schatzenheimer Gang. However, recent events have complicated matters considerably. Following a series of inter-gang disputes, the Valantinas staged a carefully planned and devastating raid on the Schatzenheimers. The Schatzenheimers were wiped out and the gem - along with everything else of value - was taken by Emilio Valantina, the mob's 'god-father'.

Dirck Huydermans, fearing his smuggling operation would be next on the Valantinas' list, sent an Assassin by the name of Jan Hoogen to kill Emilio. Jan entered Emilio's apartment via a secret entrance from the sewers, brutally murdered him and hacked off his head as proof of the deed. He then searched Emilio's corpse and found the gem. After hastily searching Emilio's apartment, Jan went back into the mines taking the stone and Emilio's head with him.

Jan never made it to the Huydermans' base. On the way back he was attacked by a Swarm of Rats. He was finally cornered in an old mine wagon, used by the Huydermans for transporting contraband, where his body - and the gem - now lie.

Just before the players' arrival, the Huydermans caverns were invaded by followers of Nurgle. They are still there, awaiting reinforcements and being held at bay by the remnants of the Huydermans gang. The cultists know the gem is somewhere in the Asylum, and they will stop at nothing to find it.

The Huydermans sent one of their number to fetch help from the Valantinas, who by now have realised the truth about the gem. They killed the messenger and are now preparing to evacuate their headquarters rather than risk infection.