A 21-year-old woman is admitted after 10 days of insomnia, paranoia and disorganised speech. During the next 48 hours she develops lip-smacking and tongue movements, a generalised seizure, fluctuating blood pressure and increasing somnolence. Her normal brain MRI is initially reported as reassuring. The experienced nurse does not let the psychiatric admission, the normal MRI or the absence of a persistent fever close the assessment. The combination of rapid psychiatric change, orofacial dyskinesia, seizure, reduced consciousness and autonomic dysfunction meets several of the symptom groups used for probable anti-NMDA receptor encephalitis. The immediate priority is airway and cardiorespiratory assessment, continuous monitoring and seizure safety; the diagnostic priority is CSF plus serum testing, EEG and exclusion of infection and other mimics. A normal MRI does not remove the diagnosis. The team should begin the Canadian three-step tumour search, including pelvic imaging for an ovarian teratoma, while autoimmune neurology reviews the antibody testing strategy. If the patient continues to deteriorate, immunotherapy should not be postponed until the laboratory report returns. A falling respiratory rate, rising end-tidal carbon dioxide or worsening airway protection...