After surviving their first adventures, the protagonist and his/her girlfriend Ann are no longer protecting the ancient sphere that reveals the future, and are now free to escape the cursed town and return to the world of the living. As they do so, a series of mysterious events separate the lovers, forcing them to fight once more the dark forces entrapping the city.
Lost in the City: Post Scriptum is a hidden object game with some elements borrowed from traditional point-and-click adventures. The player assumes the role of the protagonist, seeing the world from his/her perspective. The main objective is to gather a series of items to solve all the puzzles found on the many locations, by dragging and dropping them from the inventory at the bottom to an interactive hotspot on the scenery to perform an action or complete a task.
Most of the necessary items are received after completing one of the hidden object challenges, taking place on a separate screen cluttered with assorted paraphernalia scattered around the scene, where all the entries from a list at the left side have to be found and clicked. A magnifying glass can be summoned with a right-click, or by selecting its icon at the bottom-right corner, replacing the cursor and enlarging portions of the screen to make the search for small objects easier. The hint button is a S.O.S. sign at the bottom-right, showing the position of one of the required items, but taking sixty seconds to recharge after use. Extra hints can be collected as pink butterflies concealed on the hidden object scenes.
When moving between locations, a mini-adventure takes place inside a window at the center of the screen, where the player has to choose one of the multiple options available in a similar fashion to the Choose-Your-Own-Adventure books, but always with the same outcome. Some locations have self-contained puzzles, where mechanisms and pieces have to be manipulated directly to open safes, reassemble train tickets, and complete other similar challenges.