Like the previous game, The Room: Old Sins is a variation on room escape game, where the player is presented with a very detailed dollhouse to examine and discover the secrets therein by manipulating objects in it and solve its puzzles. Part of this puzzle involves interacting with the unique material known as Null, which has the ability to warp reality. Using a special eyepiece, the player can see objects made of Null, with objects that are hidden or puzzles seen through Null item. Items can be collected and examined, and in some cases, manipulated to reveal another object or preparing items to be used in the puzzle. If a player becomes stuck, the game provides a hint system, where after a certain time, a player can ask for directions; there is no penalty for using it.
Unlike previous games, where players work their way through a series of rooms with one or more puzzles in each, dollhouse of Sin Old prize some puzzles that are interconnected among several rooms of the house. players can have up to three different rooms and the exterior of the dollhouse to solve each puzzle, with new rooms being accessible through the course of the game. There are elements interconnected puzzle between this room; for example, water that is being pumped into the kitchen to be heated to produce steam needed to power equipment in the workshop. Each room contains a special artifacts as the ultimate "gift" her. After these artifacts are collected, the room followed by an evil entity associated with Null, so it is no longer accessible
At the turn of the 20th century, the player character enters Waldegrave Manor, looking for any clues to wealthy couple who lived there: Edward, an engineer ambitious, and Abigail, the wife of a high-society. The only item of interest was found is the detailed dolls, mirroring Waldegrave Manor, in the attic. As the player-character check dollhouse, they found a note left by Edward and Abigail, detailing their fate. Edward has received a piece of Null and took great interest in studying it, devoting more and more time to that of Abigail. Abigail recognized that the work of Edward with Null it plays second thoughts and the reality of their home, and tried to pull him away from his work. After he was attacked when he got in the way, he took the Null and hid it in a dollhouse in the attic Manor and then fled. Edward, driven mad by Null, searching frantically through the house to Abigail or Null, but was never able to escape themselves for reality-warping power of Null that caused him to be trapped in a recursive loop between the house and Manor. He finally realized that Null hidden in the doll house but could not find a way to open it, and let the evil power drawn by Null to take his life.
The player-character discovers the body of Edward dollhouse and were able to open it to find hidden inside Null pieces, placing them in a special compartment of their toolkit. Once removed, converts to a toy doll more commonplace. The player-character is revealed to be members of the Circle, a secret organization that collects various pieces Null found previously; the actual task of the player is to find Null discovered by Edward. Narrative reveals that the members of the Circle should have been more alert to Abigail to have insight on how to hide from Edward Null.
