One murky night in Lankhmar, Fissif and Slevyas, members of the Thieves' Guild, steal valuable jewels from Jengao the gem merchant. Whilst returning to Thieves' House, they are ambushed and attacked by Gray Mouser and Fafhrd simultaneously, who steal the gems. Recognising kindred spirits, they agree to share the loot. They return to Mouser's lodgings, where Fafhrd is introduced to Mouser's woman Ivrian and Ivrian meets Fafhrd's woman, Vlana.
Somewhat drunk, Mouser persuades Fafhrd to join him in a quest to infiltrate the headquarters of the Thieves' Guild, in the guise of members of the Beggar's Guild. They are initially successful, but their disguise comes unstuck when their glib story is seen through by Krovas, Grandmaster of the Thieves, and the Beggarmaster. Fleeing, they return to Mouser's hovel, only to find to their horror that both girls have been killed and partially eaten by giant rats and by Slivikin, a fast-moving evil witch-beast conjured up by Krovas's warlock, Hristomilo.
In grief and anger, they return to Thieves' House and charge in, causing panic and chaos. They kill Hristomilo, then flee from the city.