"Bones" season 11 episode 17 opened with a drunken man in the forest who stumbles upon a body in acidic goo.

Hodgins discovers that the body is covered in muriatic acid and has no internal organs. However, a special metal clip implanted in the body catches Aubrey's attention. As she recognizes it as a government-issued clip for the Secret Service, they immediately reports it to Agent Walker, who then confirms that an agent named Graham Roberts has been missing for quite some time.

Pulling out x-rays from the medical files of Roberts, Fisher finds out that the shrapnel found in a fracture in his femur is a match between ante-mortem and postmortem x-rays. Also, further investigation leads Agent Patel to believe that the victim may have been near a landscaping business before his death, and that the killer is a trained shooter. Brennan also concludes that the perpetrator used his elbow or knee to hit Roberts' temple, and that he is left-handed.

As the investigation progresses, Booth realizes that Agent Walker is left-handed and a member of the Seal. Booth tries to approach Walker, but just when he is about to do so, Aubrey notices Neil Stockton in the crowd while the motorcade of the president temporarily halts for hand-shaking. After a while, a big commotion besets the crowd, and shots start to ring out. Neil goes for the president, but Walker protects him to the extent of losing his own life. Booth then takes out Neil.

Towards the end of the episode, the autopsy of Walker reveals that an incident in the past caused a blood clot to form in his brain, making him paranoid and confused. Saroyan and Booth suspect that Agent Roberts might have asked Walker to step down, but the paranoid Walker thought that Roberts was simply trying to compromise the Secret Service so he murdered him.