Just us having some fun with a studio we are friends with and who have also made a great co-op game.” There is a little cameo from one of the L4D characters (the comic should give you a hint) and a fun little easter egg with a payoff later in Left 4 Dead. It is not telling the origins of the Infection and is not canon. “This is a 100% Overkill made mission for Payday: Heist simply set in no mercy hospital from the Left 4 Dead series. Update: In an e-mail exchange with Kotaku, Valve’s Chet Faliszek gave some details on PAYDAY: No Mercy.