Don's errand

Don't screw with Don
Since you likely don't have any money on you yet, you can't just buy a passage. However, guy standing nearby talks something about other way — through the sewers. Eww. After following through the sewers, Lust Doll reaches Slums.

The only exit from here is guarded by toll guy who demands $5 for every passage. To progress further, Lust Doll must somehow get past him without paying — either by at least 5 Strength to push him, or at least 5 Speech to trick him.

After resting and revisiting Slums, Don's guys would find you and bring back to Don, who would demand not just the money you didn't pay, but also "fee", resulting in $200 "fine" this time. Paying up would just reset him, as would saying what you are broke (though this would unlock "hidden" sex scene), so to progress up you need to refuse and offer to work it up instead.

Runaway pet
Don doesn't need assassins, so it would be either sex work or grunt work. Sex work opens additional scenes (this is repeatable event as long as you don't progress further on this quest), but story would only progress further after you accept grunt work. Choosing to resist at the start, but backing up after Don admits what you have guts would result in you automatically picking grunt work.

"Grunt work" is simple – find one particular cat-girl, runaway sex slave, and bring back "his property".

If you still didn't make it into Cassie's safehouse, do it now.

Despite all attempts to warn Cassie, this amounts to nothing: Don decided to not trust you, and just sent his men to follow you and learn where Cassie hides; the moment you would go to sleep, Cassie would be abducted.

When you would re-visit Don, he would offer you $500 as "reward. You can accept or refuse, but it wouldn't affect subsequent plot in any way.