The Anubis Gates by Tim Powers

The book begins with Egyptian sorcerers and gypsies, quickly branches into time travel, and Coleridge. A scholar from 1983 finds himself in London in the 1810, where he, broke and friendless, finds magical and non-magical enemies--and he knows a few key facts about a few key people. (The creature isn't a werewolf--it would be a nicer being if it were.)

The plot is fast and complex, with a heavy dose of Egyptian mythology/magic and attention to detail. Powers plays fair with the reader.

I'm afraid I didn't like it as well as it deserves. You might.