To the desert

This quest becomes available after saving Cassie from the Don. It initiates when Lust Doll asks Cassie what the Don meant when saying that he'd "bought" Cassie; turns out, she used to be a slave, and he'd bought her in some town in the middle of a desert.

Learning directions
Realising that the only person who may help them with finding the town is the Don himself, Lust Doll decides to ask him. It's of no use to try to enter his residence, you wouldn't be allowed inside, but there's a simpler way: as Arlene is the Don's dominatrix, she can be asked to arrange for your meeting during one of their sessions; just talk to her either in The Torture Rack or at Police Station.

The plan works; while the Don tries to refuse talking, Arlene simply forces him, and he reluctantly gives the map with directions towards the town, as well as shares information how to find the Desert itself.

Finding the town
The Desert gradually drains your stamina, with amount of stamina gradually increasing, until you succumb and faint, which would send you to the last respawn point.

The map would guide you to the town, just follow directions. First three rows tells how to reach the next oasis (where you regain lost stamina and reset stamina draining back to default value), while the fourth one leads to the town; next row's path starts where the previous one's ended. Note that desert edge isn't a part of the coordinate system, you should start counting steps from location directly above it.
 * West 2, North 4
 * East 4 North 3
 * West 3, North 4
 * East 1 North 4