80's/90's Private Detective novel: gun with 4-dimensional clip, protagonist retrieves an alien artifact and escapes gas exhaled by a corpse

Question

I don't really remember much about this. The main character was a private detective. He had a gun with a 4 dimensional clip, that held 100,000 rounds.

At one point during the story, he has to enter a secret, government, underground laboratory and retrieve an alien artifact. When he reaches the bottom level, he finds all the personnel are dead. Their bodies are withered and leathery-looking.

He finds the artifact and is leaving, when one of the corpses exhales a cloud of green, glittering gas. The other corpses begin to do the same. He panics and runs for the elevator. The gas follows him. As the elevator is returning to the surface, the gas begins to seep through the door. In desperation, he grabs the fire extinguisher and sprays the gas with it. The gas retreats and he escapes.

Answer 1

This sounds very much like a Simon R. Green book, probably from the Secret History series. Eddie Drood has a Colt Repeater, a gun that teleports bullets directly from... somewhere, so it never runs out. He keeps it in a pocket dimension in his coat.

In Property of a Lady Faire (2014), he is looking for an artifact, (the Eye, I believe) and it was in the Department of the Uncanny (Govt Organization)... When he gets there, everyone is dead.

Unfortunately, having read the entire series, I'm not positive that is the correct book (the books tend to reference previous ones at times).

I also don't recall the green gas part, but it's possible I missed that while skimming my copy. (or I could be totally wrong altogether)