Jem Barbary becomes a bogler's apprentice in 1870's London and gets the fright of his life in a city where science clashes with superstition and monsters lurk in every alley.

Ned Roach becomes a bogler's apprentice as Victorian London seeks to banish its bogle infestation once and for all in this conclusion to the trilogy featuring young assistants to Victorian London's best monster catcher, Alfred Bunce.