Sidekicks (The Enemies Trilogy Book 3)
by P.K. Gardner
When Good Guy is murdered, it's up to his sidekick to fill the void. But Ajax Gadzinski more interested in avenging his friend than joining the long line of heroes who died for the cause. Besides, if the rumors are true, the original Good Guy is back, saving people like he never left.
Or, you know, it could just be the evil twin.