Aliens have appeared all over Earth in large spaceships. For months, they did nothing but sit there, until one day humans emerged from them and said they had been abducted in the years prior, and would now serve to be translators. Avery is a commercial driver who gets a call from her boss who has a contract with one of the aliens. She is to drive the alien wherever it wishes inside the United States. Before she picks up the alien and his translator, she is stopped by a likely-FBI agent, Henry, who wants her to spy on the alien. She tells him she doesn't spy on her clients, but she will call him if she thinks the country is in danger.

Avery soon learns about the human translator, Lionel, and his relationship with the alien. As it turns out, the aliens are not conscious; they are sentient, but lack a conscious self. Via a complex process of neurotransmission, these unconscious aliens gain conscious experience through their human "hosts." So, Lionel always has two unconsciouses: his own, and his alien's. The alien just wants to see what humans are like when they live their own life and get more conscious experience; to them, it is like a drug, but it is killing them. Avery takes Lionel and the alien to several different places; a public library, a state fair, national parks and campgrounds. They have to be careful, because there is a lot of suspicion around the identity and will of the "translators" like Lionel. His face is all over the news in some places.

Eventually, Lionel tells Avery that the alien is dying, and that he wants to take it to a quiet place to die. Avery drives him to a cemetery, where her late infant daughter is also buried. The alien -- which looks like a piece of coral -- dies and dissolves into the soil. Lionel tells Avery that the alien will go through some cycles of spores and new growth, and then will "infect" dogs or children that come along. Avery and Lionel grab some of the "infected" dirt for themselves, wanting to start the alien invasion.