Beyond the blue moon - Simon R. Green

Captains Hawk and Fisher are the only honest cops in the down and dirty magical city of Haven. In a place where anything can be bought, stolen or fought for, they've stood up for decency and right; together, they have taken on everything from vampires and werewolves to conniving politicians. They've solved locked-room mysteries and dealt with the enigmatic Beings on the Street of Gods.

But now it's their last case as members of Haven's City Guard, and all hell is breaking loose - because they're not leaving town without doing a little cleaning up first. The bad guys are going down, whatever it takes.
Meanwhile, back in the Forest Kingdom, King Harald has been assassinated and the call has gone out to Prince Rupert and Princess Julia, to return to the Land they once called home, to bring a murderer to justice.