Five adventures from one issue of Dungeon. Five. This is the fifth module in the issue that seemed worth talking about in regard to fitting it to a Ptolus campaign.
Central to the story are a group of evil Skulks that have stepped up their robbery and murder efforts. This has the City Watch thinking the thieves guild has gotten bold, and the Watch plans to crack down.
The PCs can become enmeshed in the situation through a number of approaches. The Watch can hire them because their own men are stretched thin and there's some urgency to get things resolved. Or they might owe a Watch Captain a favor. Maybe someone they know was a victim and they decide to investigate.
The thieves guild has enacted a plan to put an end to these skulks plans by luring the Watch right to them. They have a doppleganger find and ally with the Skulks to fool them into thinking they're working for the guild and push them to greater, riskier activity.
It might be interesting to have the Killraven Crime League be the ones trying to set the Skulks up to take a fall in order to get rid of minor competition and take some heat off of their people in the district.
As written, part of the action takes place in the sewers below the Docks District, but in Ptolus there's nothing below the docks except deep water. The district itself is a construct partially held up by magic. This means we need to move that activity to another location.
If you have the Skulk bandits operating in Oldtown it would ruffle enough feathers to get the Watch working hard to find the perpetrators. It also opens up the possibility that the characters might go to Skulk Alley seeking insight. This could prove interesting because it's not certain that these Skulks would rat out the others. In fact, if they know about the plans to deliberately have them hunted down by the law, they might do some misdirection.
The Skulk bandits are operating out of a hidden lair reached through the sewers. This old lair was once used by criminals who worshipped a deity of shadows and thievery. Based on the bloodstained altar and other factors the best choice is Maleskari.
Years ago some members of the City Watch raided this location and sealed some of the occupants inside a section the Skulks haven't broken into yet. Those occupants died and turned into ghouls and ghasts. Why they were stuck inside is a mystery since there's another access point down a set of spiral stairs descending several hundred feet into a set of catacombs and passages the author left undetailed so DMs could fill in what lies below. You can either plan ahead for why they couldn't escape or omit the stairs altogether.