That Valve/Overkill Software collaboration that no one seems to be talking about has been revealed as a PAYDAY heist DLC level set in Left 4 Dead’s Mercy Hospital. It’s being called PAYDAY: No Mercy.

A debut trailer has surfaced which you can watch below. Details are still a little thin on the ground but if you watch the teaser below you should be able to make out a few L4D references.

Valve’s Chet Faliszek has reportedly commented on the trailer and has cleared up a few questions and preceptions of that No Mercy will entail.

“This is a 100% Overkill made mission for Payday: Heist simply set in no mercy hospital from the Left 4 Dead series. It is not telling the origins of the Infection and is not canon. 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. Just us having some fun with a studio we are friends with and who have also made a great co-op game.”

No date and no formats are known as of yet.