Portal of the Gods — John Rickards

Step through and it can give you back everything you've lost, or take away everything you've got.

Jack Harker's a washed-up adventure junkie with a knack for languages and getting himself in trouble. But when armed strangers break into his house looking for his parents' old notes on the legendary lost city of Huayacapo, they inadvertently draw him into a secret war that's been raging for a century and a half, a shadow conflict to unearth the past, and to control the future.

His enemies are after a relic of a pre-human civilization, the gateway through which the gods themselves supposedly entered the world, a door to other worlds, other times. They have other artifacts bonded to them, enhancing their abilities and extending their lives. They have relentless, inhuman servitors who obey their every command. They have limitless wealth and wield vast influence over governments and civic authorities. Jack's only allies are revenge-driven thief Anya Martinez, his crazy uncle, and a secret group who may not even exist.

Beating them to the prize will take luck and cunning, and the race will lead from the Florida swamps to the Andean foothills to a buried Nazi facility in Antarctica.

And it's not just the bad guys Jack and Anya have to deal with: this isn't the first time someone's activated the portal, and the shadows of those who tried it last could slaughter them all if the gate is opened again.