The protagonist wakes up in a hotel room in midtown Manhattan with no clothes and no money, and what is worse, no memory. Soon he discovers that some man wants to kill him and he is wanted for murder in Texas. Now his quest is to find out what exactly is going on, who he is and how to set things right.
The defining feature of Amnesia is the inclusion of the whole of Manhattan, more specifically about 4000 separate locations, 650 streets and the subway system. For this reason the original package includes a map and the "X-Street Indexer" (a code wheel for finding the nearest cross street when aligning the avenue name with the street address number), so that the player can find his way.
The game also simulates the time of day which, for example, means that stores close and open at the correct time. Most puzzles are inventory or conversation-based and it is often required to be at right place at the right time. Additionally the player needs to take care about surviving, so he needs to take jobs to earn money, buy food and find shelter at night. This is represented by the score which is divided into three parts: detective (plot advancement), character (how he interacts with Manhattan's citizens) and survivor.