Trouble in the Old City

Publisher's blurb: The town of Ylraphon on the border of the Flooded Forest has been targeted by the yuan-ti. One of them has uncovered an ancient ritual to change the people of the area called the Old City into their servants. Can the adventurers stop the yuan-ti in time? The whole of the Moonsea may be at risk if they fail. A 2-hour adventure for 1st-4th level characters (optimized for 3rd level)