Murdoch Mysteries: Nightmare on Queen Street S01E05 - Chapter Five: The Vanishing Policeman

You have made significant progress in your investigation - with Doctor Grace's help, you've established that both James Danby, as well as Rebecca Foster's mother Mary were killed the same way - via a circular wound to the forhead, and both murders were concealed by staged injuries. However, you've made no progress on Rebecca's song, only that the notes C-DDDD-FF-B don't seem to match any known tune. But now, the unthinkable has happened! Detective Murdoch has been abducted by some unknown party. Your investigation is on hold until he is found.