Penumbra is something that covers, surrounds, or obscures as in a shroud. Penumbra Overture, hereby known as "PO" is an adventure game by Frictional Games that lives up to this characterization. PO begins with a plea from Philip and has your character following in his footsteps by purchasing a ticket on a tramp steamer to Greenland. But what exactly is this mystery about? Frictional Games is not telling; that's for you to discover.