Sherlock Holmes + Vikings + Dragons = plot problems...

Right. I've started writing a Holmes-inspired (and heavily based) VIking detective story, but I'm having issues.
Basically, for the first half or so the crimes are steadily going to build up until a Moriarty-esque dragon is revealed to have been behind it. There will then be a Final Problem-like bit where Holmes comes up against the dragon and fakes his own death.
The rest of the book will be set some time later, with Holmes returning to find that Watson (his slave) has been put to death for his supposed murder. He's then forced to choose between leaving Watson dead and sacrificing Mrs. Hudson to bring him back. He sorts something clever out.
The problem is I then need to have more crimes and then conclude it satisfyingly somehow. But... How? What can I do that's bigger and better than Moriarty-Dragon?

I need more info to help you here, sorry. What are the other crimes/problems? Oh and the Norse word for 'Slave' is 'Trell'.

Thrall's the easiest anglicisation I think.
I haven't actually worked those out yet, but they'll mostly be thefts/murders. I just need some sort of villain that's one bigger than a Moriarty-Dragon :/

Maybe some sort of god of death? Your Viking Holmes would have to fight/trick it to get his Watson back.

Looks like it'll end up with Holmes vs Loki... Now I just need to work out how to dispose of Loki.

Well, Norse gods CAN die...

So this is actually Sherlock Holmes in the viking world?