Gameitall 
Ever wonder how the zombie outbreak of Left 4 Dead started? So did the guys at Overkill Software, the creators behind Payday – The Heist, and it looks like they’re going to get the chance to tell the story.
A trailer was leaked (and then pulled down from the studio) stating a collaboration between Overkill and Valve revealed Payday: The Heist – No Mercy. It revealed that the episode will act as a prequel for the zombie shooter in which the robbers are breaking in to L4D’s Mercy Hospital.
The Youtube description stated “Have you ever wondered how the Left 4 Dead series began? It started with a Heist!” which likely means that the player will be the cause of the Zombie Apocalypse. OverKill and Valve has not mentioned if the game will be a stand-alone game or as DLC.
Speculation of it being a PC exclusive has been risen since on consoles, Left 4 Dead has only been on Xbox, while Payday has only been on the PS3, leaving the PC the only device that has both games available.
