Michael treats an 18-year-old Indian-American man who has been suffering from headaches as well as hearing a voice coming from inside his head. Brain surgery reveals that the patient had a chimera - the remnants of a twin that was absorbed into his body in utero. Michael is able to successfully remove the chimera, but the voice inside his patient's head gets worse. Does he have his own 'Anna,' the spirit of a twin brother stuck inside his mind? At the Clinica, it is Kate Sykora's first day in charge and things start with a bang as a car accidentally drives through the front wall. No one seems seriously hurt at first, but the driver's daughter starts developing symptoms of a herniating brain. With time running out, Kate has no choice but to call Michael for help.