The Fire in the Sky (S05E14)

William chases his daughter Charlotte through the dark woods behind his house. His vision distorts and he falls to his knees. The next day, Father Brown and Mrs. McCarthy visit a disorientated William who says that Charlotte's gone. Later Charlotte staggers into the police station, shouting that 'it's trying to get out.' She loses consciousness and is taken to Kembleford Cottage Hospital where Dr. Ashley and nurse Alisha treat her. (iTunes)