The Dragon Gate Omnibus Volumes 1-3

He swore an oath to protect all life. Now he must kill to survive. Being a knight at the Renaissance Festival is easy, but when Ryan is magically kidnapped to another world, the quest he must do might leave him dead. Mistaken for a dragon-slaying knight, he must kill the dragon queen to be sent home. At least he is not alone. Three of his friends are kidnapped beside him, all of them mistaken for the Ellorian Champions.
The real heroes have been missing for years, but they may hold the key to keeping everyone alive.