"Head On" is a science fiction novel written by John Scalzi. The story is set in a future where people can transfer their consciousness into new bodies, known as "threeps". The protagonist, Chris Shane, is a former professional athlete who now works as a "Haden's" agent, investigating crimes committed by people who use threeps as their bodies. When a murder case involving a Haden's threep is assigned to Chris, he must navigate through a web of political intrigue and personal vendettas to uncover the truth behind the crime. As Chris delves deeper into the investigation, he realizes that the case is more complex than he initially thought, and he must use all his skills and resources to solve it before it's too late.