(Get out your best cynical jokes – here comes the third-person narrator.)
It's a nervous night around the law courts for some reason.
Mr. Weevle is pacing in his room at Krook's. He looks out the window and sees Snagsby, who is still all discombobulated from being a small part of the Jo mystery.
They chat about the dead guy that used to live in Weevle's room. Weevle is a huge fan of this morbid conversation, as you can imagine.
Finally Snagsby goes away, followed by a disguised Mrs. Snagsby. She is apparently still spying on him.
As soon as he leaves, Guppy pops out. Evidently he's late for the meeting he and Weevle were planning.
They start whispering and plotting. It becomes clear that Guppy doesn't actually have the letters he told Lady Dedlock about. Krook has them and is supposed to hand them over to Tony (Weevle) at midnight to help him read them, at which point Guppy will steal them.
They're kind of pathetic criminals, if what they're planning to do can even be considered a crime in the first place (since Krook stole the letters from the dead Nemo).
Both are freaking out about being in the scary room in the middle of night. Tony is particularly nervous and worried.
All of a sudden some kind of gook and nasty gunk starts falling around them in the room. Since it's midnight, Tony goes down to see Krook.
At first he finds nothing but some kind of grease and oil all over the place.
When they shine a lamp around they discover... Krook's cat eating his remains! Krook is dead! And he died of... spontaneous combustion!
(OK, this nonsense was mocked hardcore when this novel first came out. But Dickens defended the idea saying basically, "well, I think it could happen," without offering much evidence. So OK. The man was a genius. We'll cut him a little slack in the spontaneous combustion department.)