Here we have a twisted plot by a rich merchant to gain even more wealth and to ruin two other merchant families by setting them at each other's throats in open conflict. With some work, it definitely fits into a Ptolus campaign.
The party would encounter the scoundrel in the story being vastly outnumbered by gang members (it doesn't say, but he likely hired them himself), and in a fight for his life down a side ally, probably near or on Tavern Row. The well-off young man is injured (he has to make it look convincing) and needs help. Assuming the player characters come to his aid, the gang will quickly find themselves outmatched and run off.
The beneficiary of their rescue effort offers to reward them with drinks and dinner at a fine restaurant where after a little time he mentions an offer to hire their help with a friend's problem. His friend is also a merchant and is in love with the daughter of another well heeled merchant. The daughter loves him back and wishes for them to be together, but her family won't hear of it, instead planning to marry her off to someone she despises. The wedding is due in a couple of days.
The job then is to kidnap the girl before she can be married off and bring her to a specific park to wed his friend. You can figure out which park in the city to use or even make one up. He makes a generous offer of money, bolstered with the offer to get them whatever supplies, documents, uniforms, or other items they may need for their plan. If asked, you can have him explain he'll more than make his money back from a lifetime of business deals with his friend.
If accepted, he provides the PCs with the target's physical description and her typical schedule at home (he has inside contacts), and that she frequently goes shopping in South Market at upscale shops in the afternoons.
She is not aware of the plan and if asked who sent them, tell her the boyfriend's name so that she'll remain calm. The party is to bring her to the park an hour before midnight of the day she was to be wed.
If played right this will all sound to be on the up and up. There are other possible hitches in this story. Her cousin happens to be in town at the right time and place to be kidnaped in her stead. The details in the adventure explain how this occurrence throws a monkey-wrench into the plan, possibly exposing some deception afoot.
Of course the scoundrel has planned to murder the young lady and frame his "friend" for the deed.
The districts most likely used here include the Guildsman District, South Market, and Midtown. The thought was to use The Mane as the park, but it is the home of most of the city's Litorian population leaving a bunch of witnesses. Something closer to the Guildsman District would serve better.
As this is a heist operation, listening to the players plan how their characters will do it should be enjoyable for the DM.