: If you haven't already, download and install the Steam Client .
: KoukouStudios lists official purchase options through Steam , Green Man Gaming , and the Humble Store . Lethe - Episode One Download PC Game
: If you bought a key from a third party (like Humble or Green Man Gaming), go to the "Games" menu at the top of Steam and select "Activate a Product on Steam..." to enter your code. : If you haven't already, download and install