Grendel is a troll who comes up from the world below to find love. But the passage is hard, and it's only with the aid of a human named Ken that Grendel survives. Ken, a successful, thirty-ish software engineer, lives peacefully in the suburbs with his dog Jake. Though six feet tall, Ken has always secretly dreamed of meeting a man bigger than himself. In Grendel he finds this desire met in spectacular fashion.
Grendel is attracted to Ken too, but before the pair have time to explore their feelings, an agent from the Federal Bureau of Geostasis arrives. He tells Ken the FBG have detected Grendel's passage, which is a breach of security. They want to take Grendel into custody and send him to work in the mines. Ken defies the agent even though he knows it will lead to trouble. If Ken and Grendel are to have any possibility of staying together, they must find some way to elude these government forces.
A whole new world is opening up for Ken, who always viewed himself as a law-abiding person. He feels helpless, but Grendel has some ideas about how to elude the FBG and stay together.