Norwegian heart of darkness
The leopard is a whopper of a book weighing in at over 700 pages. It may be massive but it's a hugely enjoyable read if you can get past the first few violent pages. In Oslo there is a serial killer on the loose, Harry Hole, is hiding in Hong Kong, and the two main criminal agencies in Norway are at war with each other. Harry must be retrieved if the killing is to stop. But who is the murderer? And what is his motivation?
Moving at breakneck speed from Hong Kong to Norway to the Congo and back and forth again; this is a cracking read. It may help if you've already read Nesbo's acclaimed thriller The snowman (I hadn't) as it does have some bearing on this book, but you can get by without it.
The plot is complex, but not so intricate that it completely loses the reader. There's a truly evil bad guy, well up on the Hannibal Lector scale of nastiness; while Harry Hole is a truly Miltonic figure, a sort of Lucifer "naughty-but-nice" guy.
If you've never read Jo Nesbo before this would be a great place to start. Get past the first few video nasty style pages and you won't be able to stop reading.