Defender

The fourth novel in J David Baxter's epic portal fantasy series, the Greymantle Chronicles.
Having returned to Earth from Greymantle's past with the skills needed to save his friends, he is confronted by unexpected discoveries that make him question everything he thought he knew about the world he was born on. When he returns to Greymantle with an unexpected passenger, he will need to overcome guild rivalries and infiltrate the enemy organization to put all the pieces into place to save his friends and his love. If it all goes according to plan, Nate will have his long-awaited confrontation with the bleeder agent who spent months trying to assassinate him and kill those he cares about!
Set in Greymantle, a unique world of swords and magic that is medieval in flavor but seen through the lens of a modern college student from Earth, the Greymantle Chronicles are an epic fantasy series on a high magic fantasy world where technology and science never existed. Yet, cities are cleaner, banking is done with magic tokens, floating carts are used to haul freight, and magic is a science in its own right.
Even Earth may not be as mundane as it seems despite a scarcity of mana. Now that Nate knows magic is real, he discovers that his home world has its share of magical beings, mysteries, and perhaps ancient connections to Greymantle.