Perisil had apparently had a private practice elsewhere in Adrilankha at the time Vlad sought out advice from Lady Ardwena for an appropriate advocate to represent the recalcitrant Aliera. At that point, Perisil had presumably suffered some setbacks that resulted in his taking up residence in a basement office in the House of the Iorich at the Imperial Palace. His expert knowledge of the applicable Imperial legal codes, as well as his machinations in convincing Aliera to accept him as her consul, suited him to the task of representing her case to the Imperial Justicers.
After the case was resolved, Perisil's increase in prestige following the victory in this case enabled him to return to a private practice outside the palace.
Later, Vlad had reason to again call on Perisil for legal advice related to his plan to get the Jhereg Organization to stop trying to kill him.