Dark tiger / William G. Tapply.

Enhanced descriptions from Syndetics:

Seven years ago, Stoney Calhoun woke up in a VA hospital with no memories and a series of unexplained talents (language ability, weapons expertise, etc.). Since then he's been living quietly, working as a part time fishing guide and co-owner of a local bait shop--with an unnamed visitor coming around occasionally to see if he's regained any memories. But this time, the visitor shows up looking for his help--and creating potential mayhem in Stoney's life to prove he's serious. In exchange for making those problems go away, Stoney must go to the far corner of Maine, sign on as a guide at a high end fishing lodge, and look into a couple of suspicious deaths. A govern ment 'operative' was found shot dead in a staged murder/suicide pact involving a local sixteen year old girl. Now Stoney has to uncover what the dead agent was investigating and got him killed--without being killed by the very same people.